What did the Prophet Muhammad (saw) order `Umar to do regarding his vow that he made during the Pre-Islamic period of Ignorance?
 Narrated Ibn `Umar:                     When we returned from (the battle of) Hunain, `Umar asked the Prophet about a vow which he had made during the Pre-lslamic period of Ignorance that he would perform I`tikaf. The Prophet ordered him to fulfill his vow.