Theodore the Studite
Tassin was born at Lonlay, in the Diocese of Le Mans. He was professed at the Abbey of Jumièges in 1718. United in close friendship with his brother in religion, Dom Charles-François Toustain, he collaborated with him on a new edition of the works of Theodore the Studite, which task led them to visit Rome together. Their work was interrupted by a dispute between the Benedictine Abbey of St. Ouen and the chapter of Rouen, which was supported by the erudite Jean Saas. Tassin and his friend wrote against Saas in defence of their brethren.