Prochor Moshnin, the youngest of three children of a merchant and owner of a brickyard, lost his father at the age of four, read prayer books and the life of saints at a young age and attended church services independently. At the age of 17 he went to the Cave Monastery after a pilgrimage to Kiev, at the age of 19 he entered the monastery of Sarov and took the name Seraphim. Even as a novice, his ascetic strictness was noticeable, which he practiced with iron willpower: enduring extreme cold, meagre meals without satiety and constant lack of sleep. He was ordained a priest in 1793; from then on he celebrated the divine liturgy every day. From 1794 to 1810 he lived as a hermit in the forest near Tambov, where he built a windowless hut. His daily work included constant prayer and the weekly renewed reading of all four Gospels, following the contemplative tradition of Hesychasm. In order to align himself as comprehensively as possible with God by saying the prayer of the heart, he edited his sleep even further.
The Russian Orthodox Church with Tsar Nicholas II canonized Seraphim in 1903.
Joachim Schäfer: Article Seraphim von Sarow, from the Ecumenical Dictionary of Saints – https://www.heiligenlexikon.de//BiographienS/Seraphim_von_Sarow.htm