Sayyiduna Anas (may Allah be pleased with him) narrates that it is Sunnah that when the muezzin says «‏‏‏‏حَيَّ عَلَى الْفَلَاحِ» ‏‏‏‏ in the Fajr adhan, he should say « اَلصَّلٰوۃُ خَیْرٌ مِّنَ النَّوْم» ‏‏‏‏ "Prayer is better than sleep."