When should one begin voluntary I'tikaf during the last ten nights of Ramadan?
General Chapter
Al-Mughni
Book of I'tikaf
Primary text
If one intends voluntary I'tikaf for the last ten nights of Ramadan, one opinion states that entry must be before sunset on the night preceding the twenty-first day, as the nights constitute the count of the ten nights. The first night of the ten nights is the night of the twenty-first.
Supporting text
Another narration suggests entry after the morning prayer, based on the practice of the Prophet (PBUH) praying Fajr and then entering his place of seclusion. Both rulings apply if the ten nights are vowed.