Sunnah.com reference : Book 2, Hadith 34Arabic/English book reference : Book 2, Hadith 179
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).'"
وَلِابْنِ خُزَيْمَةَ: عَنْ أَنَسٍ قَالَ: { مِنْ اَلسُّنَّةِ إِذَا قَالَ اَلْمُؤَذِّنُ فِي اَلْفَجْرِ: حَيٌّ عَلَى اَلْفَلَاحِ, قَالَ: اَلصَّلَاةُ خَيْرٌ مِنَ اَلنَّوْمِ }   1‏ .‏‏1 ‏- رواه ابن خزيمة (386)‏ بسند صحيح.‏