Musnad Ahmad Hadith 8990

It is narrated from Abu Hurairah (may Allah be pleased with him) that the Holy Prophet (ﷺ) said on the day of the Battle of Khaybar: "I will give this flag to the person who loves Allah and His Messenger, and victory of this fort will be achieved at his hands." Umar (may Allah be pleased with him) says that before this, I never had a desire for leadership, but in the hope that perhaps the Holy Prophet (ﷺ) would hand the flag to me, I began to raise my neck and look around. But when the next day came, the Holy Prophet (ﷺ) called Ali (may Allah honor his face) and handed the flag to him and said, "Fight them and do not turn your attention elsewhere until victory is achieved." So he set out, and after going a little distance, he called out and asked, "O Messenger of Allah (ﷺ), how long should I fight them?" He replied, "Until they bear witness that there is no god but Allah and Muhammad (ﷺ) is the Messenger of Allah. When they do so, they have protected their lives and property from me except for the right of this word, and their reckoning is with Allah."