(81) باب الْمُعْتَكِفِ يَعُودُ الْمَرِيضَ
Narrated Abdullah ibn Umar:
Umar (may Allah be pleased with him) took a vow in the pre-Islamic days to spend a night or a day in devotion near the Ka'bah (in the sacred mosque). He asked the Prophet (ﷺ) about it. He said: Observe i'tikaf (i.e. spend a night or a day near the Ka'bah) and fast.
Reference: Sunan Abi Dawud 2474
In-book reference: Book 14, Hadith 162
English translation: Book 13, Hadith 2468