Yahya related to me from Malik from Damra ibn Said al-Mazini fromUbaydullah ibn Abdullah ibn Utba ibn Masud that Umar ibn al-Khattabasked Abu Waqid al-Laythi what the Messenger of Allah, may Allah blesshim and grant him peace, used to recite in the prayers of Adha andFitr. He said, "He used to recite Qaf (Sura 50) and al-lnshiqaq(Sura84)."
USC-MSA web (English) reference: Book 10, Hadith 8
Arabic reference: Book 10, Hadith 438