Musnad Ahmad 31:311

Abu Amir narrated to us, Ali—meaning Ibn al-Mubarak—narrated to us, from Yahya, who said: Abu Sa’id, the freed slave of al-Mahri, narrated to me, from Abu Sa’id al-Khudri, that the Prophet, peace and blessings of Allah be upon him, sent an expedition to Lihyan of Hudhayl. He said: "Let one out of every two men go forth, and the reward shall be shared between them." Then the Messenger of Allah, peace and blessings of Allah be upon him, said: "O Allah, bless for us our mudd and our sa’, and make the blessing two blessings."