Muwatta Malik, Book 15, Hadith 14 (USC-MSA)

Yahya related to me from Malik that Abdullah ibn Dinar said, "I saw Abdullah ibn Umar prostrate twice in Surat al-Hajj (Sura 22)."

وَحَدَّثَنِي عَنْ مَالِكٍ، عَنْ عَبْدِ اللَّهِ بْنِ دِينَارٍ، أَنَّهُ قَالَ رَأَيْتُ عَبْدَ اللَّهِ بْنَ عُمَرَ يَسْجُدُ فِي سُورَةِ الْحَجِّ سَجْدَتَيْنِ ‏.‏

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also referenced under: Book 15, Hadith 486 (In-Book)