The Messenger of Allah ﷺ said, "When Bilal makes the call to prayer, eat and drink until Ibn Umm Maktum makes the call."She said, "There was nothing between the two calls except the time it took for one to come down and the other to go up."
أخبرنا يعقوب بن إبراهيم قال حدثنا حفص عن عبيد الله عن القاسم
قال رسول الله ﷺ إذا أذن بلال فكلوا واشربوا حتى يؤذن ابن أم مكتوم قالت ولم يكن بينهما إلا أن ينزل هذا ويصعد هذا
Muslim narrated it in the Book of Fasting, chapter on explaining that entering the fast begins with the rise of Fajr, etc., hadith no. 1092/38, and Bukhari narrated it in the Book of Adhan, chapter on the adhan before Fajr, hadith no. 622, from the hadith of Ubaydullah bin Umar, with this same wording. It is also found in Al-Kubra, hadith no. 1603.