Sayyiduna Abu Musa (may Allah be pleased with him) says: When the Messenger of Allah (peace and blessings be upon him) had finished with the battle of Hunayn, he sent Abu Amir (may Allah be pleased with him) as commander of a detachment towards Awtas, against Durayd bin al-Simmah. He met him, and he (Durayd) was killed, and Allah Almighty defeated his companions.
Imam al-Shafi'i (may Allah have mercy on him) says: Abu Amir (may Allah be pleased with him) was in the army of the Prophet (peace and blessings be upon him) at the battle of Hunayn. The Prophet (peace and blessings be upon him) sent him in pursuit of them. This was one army, each part of it a support for the other. When an army is of this kind, whoever gains spoils, the army and the separate detachment are both partners in it.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب السير / 17957