Sahih Muslim 1172
Sahih Muslim · Book 14: The Book of I'tikaf · I'tikaf during the last ten days of Ramadan
وَحَدَّثَنَا قُتَيْبَةُ بْنُ سَعِيدٍ ، حَدَّثَنَا لَيْثٌ ، عَنْ عُقَيْلٍ ، عَنِ الزُّهْرِيِّ ، عَنْ عُرْوَةَ ، عَنْ عَائِشَةَ ، - رضى الله عنها - أَنَّ النَّبِيَّ صلى الله عليه وسلم كَانَ يَعْتَكِفُ الْعَشْرَ الأَوَاخِرَ مِنْ رَمَضَانَ حَتَّى تَوَفَّاهُ اللَّهُ عَزَّ وَجَلَّ ثُمَّ اعْتَكَفَ أَزْوَاجُهُ مِنْ بَعْدِهِ .
'A'isha (Allah be pleased with her) reported that the Messenger of Allah (may peace he upon him) used to observe i'tikif in the last ten days of Ramadan till Allah called him back (to his heavenly home). Then his wives observed i'tikaf after him.