One document stands apart from the legends because the Besht wrote it, or dictated it, himself: the letter to his brother in law Gershon of Kutow, who had settled in the Land of Israel. Known as the Holy Epistle, it was printed in 1781 at the end of Jacob Joseph of Polnoye's Ben Porat Yosef, and manuscript copies preserve variant texts that scholars still compare. In it the Besht describes, matter of factly, an aliyat neshamah, an ascent of the soul, undertaken on Rosh Hashanah of 1746: rising through the heavenly palaces, seeing the souls of the living and the dead, and reaching at last the chamber of the Messiah. He asks the Messiah when he will come, and receives the answer that has organised Hasidic self understanding ever since: when your wellsprings burst forth to the outside, when what you have learned spreads abroad.
The letter also reports a second ascent in 1749 and practical teachings brought down from the first, above all concerning prayer: that in every letter of the words of prayer there are worlds, souls and divinity, and that one who binds himself to the letters ascends by them. Whatever one makes of the experience, the epistle fixes three things the tales cannot: that the historical Besht practised a technique of ecstatic ascent, that he understood his teaching as bound to a messianic timetable, and that the centre of that teaching was the interior of ordinary liturgical prayer.