Muwatta Malik, Book 49, Hadith 1688 (In-Book)

Yahya related to me from Malik that Abu Jafar al-Qari said, "I saw Abdullah ibn Umar drink while standing."

وَحَدَّثَنِي مَالِكٌ، عَنْ أَبِي جَعْفَرٍ الْقَارِيِّ، أَنَّهُ قَالَ رَأَيْتُ عَبْدَ اللَّهِ بْنَ عُمَرَ يَشْرَبُ قَائِمًا ‏.‏

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also referenced under: Book 49, Hadith 15 (USC-MSA)