Sahih al-Bukhari 2043
Sahih al-Bukhari · Book 33: Retiring to a Mosque for Remembrance of Allah (I'tikaf) · Vow in the pre-Islamic period to perform I'tikaf
Narrated Ibn `Umar:
حَدَّثَنَا عُبَيْدُ بْنُ إِسْمَاعِيلَ ، حَدَّثَنَا أَبُو أُسَامَةَ ، عَنْ عُبَيْدِ اللَّهِ ، عَنْ نَافِعٍ ، عَنِ ابْنِ عُمَرَ ، أَنَّ عُمَرَ ـ رضى الله عنه ـ نَذَرَ فِي الْجَاهِلِيَّةِ أَنْ يَعْتَكِفَ فِي الْمَسْجِدِ الْحَرَامِ ـ قَالَ أُرَاهُ قَالَ ـ لَيْلَةً قَالَ لَهُ رَسُولُ اللَّهِ صلى الله عليه وسلم " أَوْفِ بِنَذْرِكَ " .
that `Umar had vowed in the Pre-Islamic period to perform I`tikaf in Al-Masjid-al-Haram. (A subnarrator thinks that `Umar vowed to perform I`tikaf for one night.) Allah's Messenger (ﷺ) said to `Umar, "Fulfill your vow."