that ʿUmar had vowed in the Pre-Islamic period to perform Iʿtikaf in Al-Masjid-al-Haram. (A subnarrator thinks that ʿUmar vowed to perform Iʿtikaf for one night.) Messenger of Allah ﷺ said to ʿUmar, "Fulfill your vow."  

أَنَّ عُمَرَ ؓ نَذَرَ فِي الْجَاهِلِيَّةِ أَنْ يَعْتَكِفَ فِي الْمَسْجِدِ الْحَرَامِ قَالَ أُرَاهُ قَالَ لَيْلَةً قَالَ لَهُ رَسُولُ اللَّهِ ﷺ أَوْفِ بِنَذْرِكَ