It wasnarrated from 'Umar that he had vowed during the Ignorancedays tospend one night in I'tikaf. He asked the Prophet (ﷺ) aboutit, sohe commanded him to spend it in I'tikaf. (FR)
English reference (FR): Vol. 1, Book 7, Hadith 1772 (FR)
Arabic reference (FR): Book 7, Hadith 1844 (FR)