Jami At Tirmidhi
534
Sahih+3

Ubaidullah bin Abdullah bin Utbah narrated:"Umar bin Al-Khattab asked Abu Waqid Al-Laithi what Allah's Messenger would recite during Al-Fitr and Al-Adha, so he said: 'He would recite: Qaf, By the Glorious Quran and the Hour has drawn near, and the moon has been cleft asunder

SahihAhmad Muhammad Shakir
SahihAl-Albani