It was narrated from Mahmud bin Labid, from some men among his people who were of the Ansar, that the Messenger of Allah (ﷺ) said:
"The more you delay Fajr, the greater the reward." (RU)
English reference (RU): Vol. 1, Book 6, Hadith 550 (RU)
Arabic reference (RU): Book 6, Hadith 554 (RU)