Hadith: : :

عَنْ أَنَسٍ رَضيَ اللهُ عنه قَالَ:
مِنَ السُّنَّةِ إِذَا قَالَ الْمُؤَذِّنُ فِي أَذَانِ الْفَجْرِ حَيَّ عَلَى الْفَلَاحِ، قَالَ: الصَّلَاةُ خَيْرٌ مِنَ النَّوْمِ.
[صحيح] - [رواه ابن خزيمة والدارقطني والبيهقي] - [صحيح ابن خزيمة: 386]

Anas (may Allah be pleased with him) reported:
It is part of the Sunnah that when the muezzin says in the Adhan of the Fajr prayer: Come to success, he then says: Prayer is better than sleep.
[Authentic hadith] - [Ibn Khuzaymah - Al-Bayhaqi - Narrated by Ad-Daraqutny]

Explanation

Anas ibn Mālik (may Allah be pleased with him) reported that among what the Prophet (may Allah's peace and blessings be upon him) established in his Sunnah is that the muezzin should say during the call to the Fajr prayer, specifically after saying "Come to success", the phrase: "Prayer is better than sleep".

Benefits from the Hadith

1. His statement (it is part of the Sunnah): means it is the Sunnah of the Prophet (may Allah's peace and blessings be upon him), so it carries the ruling of a Marfū‘ (elevated) report, i.e., it is attributed to the Prophet (may Allah's peace and blessings be upon him).
2. It is recommended for the muezzin to say, in the call to the Fajr prayer, after "Come to success": "Prayer is better than sleep" twice because the Fajr prayer comes at a time when most people are asleep and rise from their sleep to pray. Therefore, this phrase is specific to Fajr and not included in the other prayer calls.