(7) باب نَذْرِ الْكَافِرِ وَمَا يَفْعَلُ فِيهِ إِذَا أَسْلَمَ
Nafi' reported:
A mention of Allah's Messenger (ﷺ) observing 'Umra from ja'rina was made before Ibn 'Umar. He said: He did not enter into the state of Ihram from that (place), and Umar had taken a vow of observing I'tikaf for a night during the days of Ignorance. The rest of the hadith is the same.
Reference: Sahih Muslim 1656 e
In-book reference: Book 27, Hadith 44
USC-MSA web (English) reference(deprecated numbering scheme): Book 15, Hadith 4076