Mukhtasar Bukhari (Abridged) 381 — Giving Fajr adhan before dawn

Sayyiduna Ibn Mas'ud (may Allah be pleased with him) narrates from the Noble Prophet (peace and blessings be upon him) that he (peace be upon him) said: "None of you should be prevented from (eating) sahur by Bilal’s (may Allah be pleased with him) call to prayer, because he gives the adhan at night so that the one among you who is praying tahajjud may return (for rest), and so that the one who is sleeping may wake up. And it is not that anyone should say that morning (has come)." And the Prophet (peace be upon him) gestured with his fingers, raising them upwards and then lowering them down, until (he showed) like this (i.e., when the whiteness spreads). (The narrator Zuhair) placed his two index fingers one over the other, then spread them to his right and left (i.e., when the whiteness spreads in all directions), then understand that morning has come.