Musnad Ahmad 833:1

Surayj and Yunus narrated to us, they said: Hammad—meaning Ibn Zayd—narrated to us, Ayyub narrated to us, from Abu Qilabah, from Malik ibn al-Huwayrith al-Laythi, who said: We came to the Prophet, may Allah bless him and grant him peace, and we were young men. He said: So we stayed with him for about twenty nights. He said to us: "If you were to return to your lands—and the Messenger of Allah, may Allah bless him and grant him peace, was merciful—and teach them." Surayj said: "And command them to pray such-and-such prayer at such-and-such time." Yunus said: "And command them to pray such-and-such prayer at such-and-such time, and such-and-such prayer at such-and-such time. So when the prayer time arrives, let one of you call the adhan for you, and let the oldest of you lead you in prayer."