Ibn Khuzaimah reported from Anas (RA):
"It is from the Sunnah that when the Mu'adhadhin says [in the first Adhan of] Fajr (prayer time): 'Haiya 'alal-Falah (Come to the success)', he says (also) 'as-Salatu khairun minan-nawm (Prayer is better than sleep).'"