Sahih Muslim Book 27, Hadith 42
When Allah's Apostle (ﷺ) came back from the Battle of Hunain, Umar asked Allah's Messenger (ﷺ) about the vow he had taken during the days of Ignorance that he would observe I'tikaf for a day. The rest of the hadith is the same.
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.
A mention of Allah's Messenger (ﷺ) observing 'Umra from ja'rina was made before Ibn 'Umar. He said: He did not enter into the state of Ihram from that (place), and Umar had taken a vow of observing I'tikaf for a night during the days of Ignorance. The rest of the hadith is the same.