Sahih Muslim 227
صحيح مسلم#227SahihIt is narrated on the authority of Abu Huraira that the Messenger of Allah (may peace and blessings be upon him) observed:Two (things) are found among men which are tantamount to unbelief: slandering one's lineage and lamentation on the dead
Scholarly Authentication
We show the most cautious grade (weakest-wins) as the overall label. Individual scholars graded it as follows:
Every narration in Sahih Muslim is accepted as Sahih (authentic) by the established status of the book.
In-book reference: 1:133