This is truly a 'tale for the ages' in every sense
The story says that there was a man named Santokh who lived in a previous yuga, who knows how many thousands of years in the past. His guru had great wisdom and was able to tell him about the intriguing ways of the future in kalyug. Among the twisted tales of the kalyug would come a great savior who would be the most important of any guru who had come before. His name would be Nanak the Guru of the kalyug. Santokh asked if he could be blessed to see the great Guru Nanak with his own eyes. He received the blessing that he would be able to survive until the time of Nanak so he drew his prana into his dasam duar and went into deep meditation. Millenia passed on and earth piled over his meditation area. When he was discovered by the Sikhs he asked if it was kalyug and if Nanak had arrived. He found out that the light of Nanak had passed to a series of successors and then, after meeting the Guru, he was liberated. Santokh was immortalized with a sarovar named after him: Santokhsar.
This is the basic version of the story I heard. Later I heard different versions of it:
-In one version his name was 'Rishi Santokh', and the master that blessed him was none other than Sita's father: Raja Janak. This would place him in the time of Lord Ram in the treta yug.
-The other version said this occurred with Guru Ram Das and that he is known as 'Baba Santokh': a saint in Sikh history.
I've always wanted to tell this story and had written a script for it many years ago. I threw this script out once I found an authentic source for the story. This was a great relief to have a proper source to help sort out the legend! It is written with great detail in the Suraj Prakash Granth. In fact, it's told in no less then 3 chapters in that volume!
The first story is the digging of the sarovar, discovery of an ancient being, his backstory and him asking deep questions to the Guru. The 2nd story is an extended katha answering those questions. The 3rd story is a continuation of the answers and then the liberation, with the help of Baba Buddha, of the yogi. With the help of Guvinder Singh we translated large portions of the 3 chapters and the following is what we found.
-His name: He is not given a name. When the Sikhs discover him they assume that he is a "Muni in samadhi". After that he is simply called "the yogi". At one point Guru ji calls him "Jogeshwar". The narration also calls him a "Maha Purkh Jogi".
-Which Guru: This story occurs in the life of Guru Arjan Dev. Suraj Prakash talks about the creation of the sarovars in Amritsar in a way that makes Guru Ram Das start the digging Himself but the project ended up being neglected and after years his digging gets obscured by overgrowth. Years later Guru Arjan then excavates Santokhsar as the first sarovar. Guru Arjan then goes to makes Amritsar the second sarovar (among the 4 he would create, the other two being Bibeksar and Ramsar).
-Guru gives a formula with safron: When Guru Arjan Dev discovers the dormant yogi he instructs that safron should be mixed with butter. This mixture is then used to massage the mysterious man's feet, and then his dasam dwar. Apparently, this restored heat in the body and allowed the man to wake up after many years. I just find this detail interesting, we don't hear many stories involving our Guru's creating such formulas.
-Baba Buddha answers his first questions: When the yogi is revived, he sees Guru Arjan and asks a couple questions: 'Who is it whom I'm looking at and what age are we in?' He was obviously trying to make sure he's landed in the right time, in the kalyug, where his master prophesied he would meet the Guru of the kalyug.
-How old was he: Baba Buddha ji answers these first questions and explains how many years of the kalyug have passed. The original writing of the Granth quotes him thusly, "barakh panchamo lakho hajara". The modern Punjabi translation instructs that this is meant to be understood as 5,000 years. This would mean that roughly 5,000 years of the kalyug had passed before the arrival of the Gurus (and we are currently about 5,500 years into Kalyug). This would mean he was minimum 5,000 or 6,000 years old. If the yogi dated to not just the previous juga duapar (as is specified in Tavrikh Guru Khalsa), but back to treta [during the time of Raja Janak], there is no telling how many thousands of years old he would then be. Could he have been 10,000 years old? Some oral traditions of this story have him all the way till Satyug and he could have been a millions years old.
-More than one Guru: As you'll see next the yogi was given the name of the 5th Guru by his master. Baba Buddha takes the time to explain who Guru Nanak, Guru Angad, Guru Amar Das were. He finished by saying "Sri Guru Ram Das continued the lineage and obliterated ignorance. Before you is his son Siri Guru Arjan. He is the 5th physical body of this light." We soon learn that the yogi may not have recognized any of the previous names but he had been told of the prophesy of the coming of Siri Guru Arjan. Meaning he had meditated on the name of Sri Guru Guru Arjan for many thousands of years.
-His back story: The yogi then explains his ancient history: he did a lot of seva for his master who attained the ability to see the past, present and the future. His master predicted that after huge passage of time 'siri guru arjan hui avtara' "Siri Guru Arjan will incarnate" and when he builds a place for tirath "then you will have his darshan". Then he was told that when he meets Siri Guru Arjan to "ask him your questions, listen well to his wisdom then you will obtain understanding."
-Baba Buddha shows him liberation: After all his questions are answered and he blissfully blossoms in perfect wisdom the ancient being goes back to his dasam duar and leaves his body. The interesting thing is that this final fulfillment is through Baba Buddha ji instead of the Guru himself. Guru ji tells Baba Buddha to fulfil the yogi's longing to be liberated. Baba ji then sits with the yogi and they both meditate together. Somehow Baba ji is able to show the path of enlightenment during their mutual meditation.
Note that there are other history sources that tell this story. Tavrikh Guru Khalsa has an alternate version where a Sikh named Bhai Sanokh was rich but had no child so his donation to the Guru was used to create Santokhsar as his child, an offspring that would live forever. Principal Satbir S. largely retells the Suraj Prakash narrative with some slight variances and also points out that Tavrikh has a different narrative.
Every version of Sikh history has certain differences. In Suraj Prakash the yogi is not called a 'Rishi' or a 'Baba' or given any name at all. It is not specified who his ancient guru was, much less if it was Raja Janak. The yogi's Guru prophesies about the 5th Guru instead of the 1st. In this version Baba Buddha plays a role of utmost importance and helps to liberate this soul through meditation. There is still a difference amongst learned Sikhs whether or not this sarovar was dug (and thus this story occurred) during the reign of the 4th or 5th Guru.
Whatever differences there may be, one thing you find about Sikh history is that the spirit pervades. The message of this story is one that teaches patience. It also unmistakably conveys the unimaginable importance of who and what the Guru is. At the end of the narration the Sikhs are flabbergasted at having seen this many thousands of years old being be unearthed, hear his ancient history, and witness him be liberated all before their eyes. These are people who had the regular darshan of the likes of saints like Baba Buddha and a Guru Arjan Dev, the personification of God!
The significance of Sikhs of that time being amazed at the ancient yogi cannot be lost on us today. It is perhaps the most important take away from this story. How blessed are we to be able to recite, and absorb, the wisdom of a Guru who a man would wait for thousands of years to see!
We can only be grateful knowing that we are able to recite the banis of such a Guru. Such a Guru who is here to save the kalyug. Such a Guru who teaches the whole world and doesn't neglect any corner of humanity. Such a Guru who can liberate souls. Such a Guru who's respected saints can also guide a soul to liberation.
To our knowledge this is the first time this detailed story has been made available to the English speaking audience.
We do hope that this story will shine upon our generations and show the world the light of the Guru. May each of us take to heart what we can as this story is so profound it could take lifetimes to understand it. Perhaps even thousands of years!