Kitāb al-Muʾmin
Hadith 9191 - وعنه (ع) قال لكُلّ شئٍ شئٌ يستريحُ إليه، وإنّ المؤمنَ يستريح إلى أخيهِ المؤمنِ كما يستريحُ الطّير ُإلى شَكله.
91. It has been reported that Abu 'Abd Allah (a.s) said: For everything, there is a thing that gives it comfort; and a believer finds rest in the company of his fellow believer just as a bird finds comfort amongst its own kind.