Mishkat al-Masabih 4 Prayer كتاب الصلاة 842

وَعَنْ كَثِيرِ بْنِ عَبْدِ اللَّهِ عَنْ أَبِيهِ عَنْ جَدِّهِ أَنَّ النَّبِيَّ صَلَّى اللَّهُ عَلَيْهِ وَسَلَّمَ كَبَّرَ فِي الْعِيدَيْنِ فِي الْأُولَى سَبْعًا قَبْلَ الْقِرَاءَةِ وَفِي الْآخِرَةِ خَمْسًا قَبْلَ الْقِرَاءَةِ. رَوَاهُ التِّرْمِذِيّ وَابْن مَاجَه والدارمي

Kathir b. ‘Abdallah on his father’s authority quoted his grandfather as saying that at the two festivals the Prophet said “God is most great” seven times in the first rak’a before reciting from the Qur’an, and five times in the last one before reciting. Tirmidhi, Ibn Majah and Darimi transmitted it.