Sahih al-Bukhari, Volume 3, Book 43, Hadith 626 (USC-MSA) ⓘ
Narrated Abu Musa: The Prophet said, "A believer to another believer is like a building whose different parts enforce each other." The Prophet then clasped his hands with the fingers interlaced (while saying that).
حَدَّثَنَا مُحَمَّدُ بْنُ الْعَلاَءِ، حَدَّثَنَا أَبُو أُسَامَةَ، عَنْ بُرَيْدٍ، عَنْ أَبِي بُرْدَةَ، عَنْ أَبِي مُوسَى ـ رضى الله عنه ـ عَنِ النَّبِيِّ صلى الله عليه وسلم قَالَ " الْمُؤْمِنُ لِلْمُؤْمِنِ كَالْبُنْيَانِ يَشُدُّ بَعْضُهُ بَعْضًا " . وَشَبَّكَ بَيْنَ أَصَابِعِهِ.
also referenced under: Book 46, Hadith 7 (In-Book) & Hadith 2446 (DarusSalam)