The Messenger of Allah ﷺ said to him, "Do not call the adhan until the dawn becomes clear to you like this," and he stretched out his hands horizontally.
حدثنا زهير بن حرب حدثنا وكيع حدثنا جعفر بن برقان عن شداد مولى عياض بن عامر
أن رسول الله ﷺ قال له لا تؤذن حتى يستبين لك الفجر هكذا ومد يديه عرضا
No references are available.
Its isnad is daif. Ibn Abu Shayba reported it, 1/214, from Waki with this chain, and Bayhaqi said, 1/384, this is mursal.