What did Prophet Muhammad (peace be upon him) do regarding `Umar bin Al-Khattab's vow to observe I`tikaf for one day during the Pre-Islamic period?
 Narrated Nafi`:                     `Umar bin Al-Khattab said, "O Allah's Apostle! I vowed to observe I`tikaf for one day during the Prelslamic period." The Prophet ordered him to fulfill his vow. `Umar gained two lady captives from the war prisoners of Hunain and he left them in some of the houses at Mecca. When Allah's Apostle freed the captives of Hunain without ransom, they came out walking in the streets. `Umar said (to his son), "O `Abdullah! See what is the matter." `Abdullah replied, "Allah's Apostle has freed the captives without ransom." He said (to him), "Go and set free those two slave girls." (Nafi` added:) Allah's Apostle did not perform the `Umra from Al-Jarana, and if he had performed the `Umra, it would not have been hidden from `Abdullah.