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Qurʾān Bukhārī Muslim Nasāʾī Abū Dāwūd Tirmidhī Ibn Mājah Mālik Aḥmad Dārimī Ḥākim Ibn Ḥibbān Ṭabarānī Nasāʾī's Kubrá Bayhaqī al-Luʾluʾ wa-al-Marjān Ibn Rajab's Fifty Riyāḍ al-Ṣāliḥīn Aḥmad's Zuhd Suyūṭī
malik:9-57 – Mālik > Zayd b. Aslam > ʿUmar b. al-Khaṭṭāb

Yahya related to me from Malik from Zayd ibn Aslam that Umar ibn al-Khattab said, "You should not pray while you are holding your bowels."  

مالك:٩-٥٧ – وَحَدَّثَنِي عَنْ مَالِكٍ عَنْ زَيْدِ بْنِ أَسْلَمَ أَنَّ عُمَرَ بْنَ الْخَطَّابِ

قَالَ لاَ يُصَلِّيَنَّ أَحَدُكُمْ وَهُوَ ضَامٌّ بَيْنَ وَرِكَيْهِ  

See similar narrations below:

Collected by Suyūṭī
suyuti:2-1662b – Zayd b. Aslam n ʿUmar b. al-Khaṭṭāb
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السيوطي:٢-١٦٦٢b –

"عَنْ زَيْدِ بْنِ أَسْلَمَ أن عُمَرَ بْنَ الْخَطَّابِ، قَال: لَا يُصَلِّى أَحَدُكُم وَهُوَ ضَامٌّ بِيْنَ وَرِكيْهِ".  

مالك