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." (DE)
English reference (DE): Vol. 1, Book 6, Hadith 550 (DE)
Arabic reference (DE): Book 6, Hadith 554 (DE)