Musnad Ahmad 770:42

Muhammad ibn Ja'far narrated to us, Shu'bah narrated to us, from Ziyad ibn 'Alaqah, who said: I heard Jarir saying, when al-Mughirah died and his relative was appointed [as governor], he stood up to deliver a sermon. Jarir said: "I advise you to fear Allah alone, with no partner, and to listen and obey until an amir comes to you. Seek forgiveness for al-Mughirah ibn Shu'bah—may Allah the Exalted forgive him—for he used to love well-being." "As for what follows: I came to the Messenger of Allah, peace and blessings of Allah be upon him, to pledge allegiance to him with this hand of mine upon Islam, and he stipulated upon me: 'And sincerity [to every Muslim].' By the Lord of this mosque, I am indeed a sincere advisor to you."