Sunan Abi Dawud 534

Zuhayr ibn Harb narrated to us: Wakiʿ narrated to us: Jaʿfar ibn Burqan narrated to us, from Shaddad, the freedman of ʿIyad ibn ʿAmir, from Bilal, that the Messenger of Allah (peace and blessings be upon him) said to him: ‘Do not call the prayer until dawn has become clear to you, like this’—and he spread his hands horizontally. Abu Dawud said: Shaddad, the freedman of ʿIyad, did not meet Bilal.