Sunan an-Nasai Book 12, Hadith 1029

أَخْبَرَنَا إِسْمَاعِيلُ بْنُ مَسْعُودٍ، قَالَ حَدَّثَنَا خَالِدُ بْنُ الْحَارِثِ، عَنْ شُعْبَةَ، عَنْ سُلَيْمَانَ، قَالَ سَمِعْتُ إِبْرَاهِيمَ، يُحَدِّثُ عَنْ عَلْقَمَةَ، وَالأَسْوَدِ، أَنَّهُمَا كَانَا مَعَ عَبْدِ اللَّهِ فِي بَيْتِهِ فَقَالَ أَصَلَّى هَؤُلاَءِ قُلْنَا نَعَمْ ‏.‏ فَأَمَّهُمَا وَقَامَ بَيْنَهُمَا بِغَيْرِ أَذَانٍ وَلاَ إِقَامَةٍ ‏.‏ قَالَ إِذَا كُنْتُمْ ثَلاَثَةً فَاصْنَعُوا هَكَذَا وَإِذَا كُنْتُمْ أَكْثَرَ مِنْ ذَلِكَ فَلْيَؤُمَّكُمْ أَحَدُكُمْ وَلْيَفْرِشْ كَفَّيْهِ عَلَى فَخِذَيْهِ فَكَأَنَّمَا أَنْظُرُ إِلَى اخْتِلاَفِ أَصَابِعِ رَسُولِ اللَّهِ صلى الله عليه وسلم ‏.‏

It was narrated from 'Alqamah and Al-Aswad that:They were with 'Abdullah in his house and he said: "Have these people prayed?" We said: "Yes." So he led them in prayer and stood between them, with no Adhan and no Iqamah, and said: "If you are three then do this, and if you are more than that then let one of you lead the others in prayer, and let him lay his hands on his thighs. It is as if I can see the fingers of the Messenger of Allah (ﷺ), interlaced