Hadith 503640
Chapter 9: Shortening the Prayer - كتاب قصر الصلاة فى السفر
وَحَدَّثَنِي عَنْ مَالِكٍ، عَنِ ابْنِ شِهَابٍ، عَنْ عُبَيْدِ اللَّهِ بْنِ عَبْدِ اللَّهِ بْنِ عُتْبَةَ، أَنَّهُ قَالَ دَخَلْتُ عَلَى عُمَرَ بْنِ الْخَطَّابِ بِالْهَاجِرَةِ فَوَجَدْتُهُ يُسَبِّحُ فَقُمْتُ وَرَاءَهُ فَقَرَّبَنِي حَتَّى جَعَلَنِي حِذَاءَهُ عَنْ يَمِينِهِ فَلَمَّا جَاءَ يَرْفَأُ تَأَخَّرْتُ فَصَفَفْنَا وَرَاءَهُ .
Yahya related to me from Malik from Ibn Shihab that Ubaydullah ibn Abdullah ibn Utba said, "I visited Umar ibn al-Khattab just before noon and found him praying a voluntary prayer. So I stood behind him, but he pulled me nearer and put me next to him, on his right hand side, and then Yarfa came and I moved back and we formed a row behind him."
Reference Muwatta Malik 503640
USC-MSA web (English) reference : Book 9, Hadith 35