مسند أحمد

It was narrated from ‘Ali (رضي الله عنه) that The Messenger of Allah (ﷺ) said: `The believers are equal in respect of blood and they are one against their enemies; protection given even by the least among them is to be honoured, but no believer is to be killed (in retaliation) for a disbeliever and no one who has a covenant is to be killed during the covenant.`