Hadith 255
Chapter 2: Musnad `Umar b. al-Khattab (ra) - مُسْنَدِ عُمَرَ بْنِ الْخَطَّابِ رَضِيَ اللَّهُ عَنْهُ
حَدَّثَنَا يَحْيَى، عَنْ عُبَيْدِ اللَّهِ، حَدَّثَنِي نَافِعٌ، عَنِ ابْنِ عُمَرَ، عَنْ عُمَرَ، رَضِيَ اللَّهُ عَنْهُ أَنَّهُ قَالَ يَا رَسُولَ اللَّهِ إِنِّي نَذَرْتُ فِي الْجَاهِلِيَّةِ أَنْ أَعْتَكِفَ فِي الْمَسْجِدِ الْحَرَامِ لَيْلَةً فَقَالَ لَهُ فَأَوْفِ بِنَذْرِكَ
It was narrated from ʼUmar that he said:
O Messenger of Allah (ﷺ), I vowed during the jahiliyyah to observe i’tikaf for one night in al-Masjid al-Haram. He said to him: “Fulfil your vow.”
Reference : Musnad Ahmad 255
In-book reference : Book 2, Hadith 169