Ahmad bin Hanbal says:
Burayrah (Aslami) has related: The Prophet (S) dispatched two regiments towards Yemen, one under the command of (Imam) ‘Ali bin Abi Talib (‘a) and the other led by Khalid bin Walid with instructions that when the two regiments are with each other they should be under the sole command of (Imam) ‘Ali (‘a), and when they are separate they will remain under different commanders. We the Muslim forces, encountered the Yemeni tribe of Bani Zayd and fought and defeated these infidels. When their men had died fighting, the families surrendered and from among the captives, (Imam) ‘Ali (‘a) chose a maid for himself.
Khalid bin Walid sent me to the Prophet with a letter informing him of this matter. I submitted the letter to the Prophet and when he had read it I saw signs of anger appear on his face. I said:
O Messenger of Allah (S), you sent me with a man instructing me to obey him, and accordingly I performed whatever duty I was ordered to do.
The Messenger of Allah (S) said:
La taqa‘ fi ‘Aliyyin fa innahu minni wa ana minhu wa huwa waliyyukum ba‘di wa innahu minni wa ana minhu wa huwa waliyyukum ba‘di (Don't try to find faults with ‘Ali, he is indeed from me and I am from him, he is your leader after me. He is from me and I am from him, he is your leader after me).1