صحيح مسلم

'Abdullah b. 'Umar reported that 'Umar b. Khattab asked the Messenger of Allah (ﷺ) as he was at ji'rana (a town near Mecca) on his way back from Ta'if: Messenger of Allah, I had taken a vow during the days of Ignorance that I would observe I'tikaf for one day in the Sacred Mosque. So what is your opinion? He said: Go and observe I'tikaf for a day. And Allah's Messenger (ﷺ) gave him a slave girl out of the one-fifth (of the spoils of war meant for the Holy Prophet). And when Allah's Messenger (inay peace be upon him) set the war prisoners free. 'Umar b. Khattab heard their voice as they were saying: Allah's Messenger (ﷺ) has set as free. He (Hadrat 'Umar) said: What is this? They said: Allah's Messenger (ﷺ) has set free the prisoners of war (which had fallen to the lot of people). Thereupon he (Hadrat 'Umar) said: Abdullah, go to that slave-girl and set her free.