Sahih Muslim Book 19, Hadith Number 4295.

Chapter : Appointment of the leaders of expeditions by the Imam and his advice to them on etiquettes of war and related matters.

Sulaiman b. Buraida reported on the authority of his father that when Allah’s Messenger (may peace be upon him) sent an Amir with a detachment he called him and advised him. The rest of the hadith is the same.