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."