Messenger of Allah ﷺ used to practice Iʿtikaf in the last ten days of the month of Ramadan.  

كَانَ رَسُولُ اللَّهِ ﷺ يَعْتَكِفُ الْعَشْرَ الأَوَاخِرَ مِنْ رَمَضَانَ  

(the wife of the Prophet) The Prophet ﷺ used to practice Iʿtikaf in the last ten days of Ramadan till he died and then his wives used to practice Iʿtikaf after him.  

زَوْجِ النَّبِيِّ ﷺ أَنَّ النَّبِيَّ ﷺ كَانَ يَعْتَكِفُ الْعَشْرَ الأَوَاخِرَ مِنْ رَمَضَانَ حَتَّى تَوَفَّاهُ اللَّهُ ثُمَّ اعْتَكَفَ أَزْوَاجُهُ مِنْ بَعْدِهِ