It was narrated from Ibn 'Umar that 'Umar had vowed -during the Jahiliyyah- to spend a day in 'Itikaf. He asked the Messenger of Allah about that, and he commanded him to perform the 'Itikaf.
Hadith ReferenceSunan an-Nasa'i / The Book of Oaths and Vows / Hadith: 3853
Hadith Gradingالألبانی:صحيح | زبیر علی زئی:صحيح مسلم