Caution: Translations of Quran and Ḥadīth may lead to possible misapplications and misinterpretations. This site is intended for students of sacred knowledge that are proficient in comprehending classical Arabic and have a strong foundation in Islamic sciences. Also note that religious injunctions rely on several aspects beyond what one may glean through reading individual aḥādīth.
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
ahmad:217 – Sulaymān b. Dāwud Abū Dāwud > Sallām / Abū al-Aḥwaṣ > Simāk b. Ḥarb > Sayyār b. al-Maʿrūr Qālasamiʿt ʿUmar Yakhṭub /

I heard 'Umar giving a khutbah, and he said: The Messenger of Allah ﷺ built this mosque and we, the Muhajireen and Ansar, were with him. If it gets too crowded, then let one of you prostrate on his brother's back. And he saw people (on one occasion) praying in the street and said: Pray in the mosque,  

أحمد:٢١٧ – حَدَّثَنَا سُلَيْمَانُ بْنُ دَاوُدَ أَبُو دَاوُدَ حَدَّثَنَا سَلَّامٌ يَعْنِي أَبَا الْأَحْوَصِ عَنْ سِمَاكِ بْنِ حَرْبٍ عَنْ سَيَّارِ بْنِ الْمَعْرُورِ

قَالَسَمِعْتُ عُمَرَ يَخْطُبُ وَهُوَ يَقُولُ إِنَّ رَسُولَ اللهِ ﷺ بَنَى هَذَا الْمَسْجِدَ وَنَحْنُ مَعَهُ الْمُهَاجِرُونَ وَالْأَنْصَارُ فَإِذَا اشْتَدَّ الزِّحَامُ فَلْيَسْجُدِ الرَّجُلُ مِنْكُمْ عَلَى ظَهْرِ أَخِيهِ وَرَأَى قَوْمًا يُصَلُّونَ فِي الطَّرِيقِ فَقَالَ صَلُّوا فِي الْمَسْجِدِ  

See similar narrations below:

Collected by Bayhaqī, Suyūṭī
bayhaqi:5629 – Abū Bakr b. Fūrak > ʿAbdullāh b. Jaʿfar > Yūnus b. Ḥabīb > Abū Dāwud > Sallām / Abū al-Aḥwaṣ > Simāk b. Ḥarb > Sayyār b. al-Maʿrūr > ʿUmar b. al-Khaṭṭāb Yakhṭub /

I heard 'Umar giving a khutbah, and he said: The Messenger of Allah ﷺ built this mosque and we, the Muhajireen and Ansar, were with him. If it gets too crowded, then let one of you prostrate on his brother's back. And he saw people (on one occasion) praying in the street and said: Pray in the mosque, (Using translation from Aḥmad 217)   

البيهقي:٥٦٢٩ – أَخْبَرَنَا أَبُو بَكْرِ بْنُ فُورَكٍ أنبأ عَبْدُ اللهِ بْنُ جَعْفَرٍ ثنا يُونُسُ بْنُ حَبِيبٍ ثنا أَبُو دَاوُدَ ثنا سَلَّامٌ يَعْنِي أَبَا الْأَحْوَصِ عَنْ سِمَاكِ بْنِ حَرْبٍ عَنْ سَيَّارِ بْنِ الْمَعْرُورِ قَالَ

سَمِعْتُ عُمَرَ بْنَ الْخَطَّابِ ؓ يَخْطُبُ وَهُوَ يَقُولُ يَا أَيُّهَا النَّاسُ إِنَّ رَسُولَ اللهِ ﷺ بَنَى هَذَا الْمَسْجِدَ وَنَحْنُ مَعَهُ وَالْمُهَاجِرُونَ وَالْأَنْصَارُ فَإِذَا اشْتَدَّ الزِّحَامُ فَلْيَسْجُدِ الرَّجُلُ مِنْكُمْ عَلَى ظَهْرِ أَخِيهِ  

suyuti:2-82b – Ysār > al-Mʿrwr > Khṭb.ā ʿMr Fqāl Yʾyhā al-Nās n
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السيوطي:٢-٨٢b –

(عن يسار، عن المعرور قال: خطبنا عمر فقال: يأيها الناس) (*): "إنَّ رَسُولَ الله ﷺ بَنَى هَذَا الْمَسْجِدَ وَنحْنُ مَعَهُ الْمُهَاجِرُونَ والأنْصَارُ، فَإِذا اشْتَدَّ الزِّحَامُ فَليَسْجد الرَّجُلُ مِنْكُمْ عَلَى ظَهْرِ أَخِيهِ، وَرَأَى قَوْمًا يُصَلُّونَ فِى الطَّرِيق فَقَالَ: صَلُّوا فِى الْمَسْجِدِ".  

[ط] الطيالسي [حم] أحمد والشاشى، [ض] ضياء المقدسي في مختاره