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