The Book of the Believer · Hadith 171 (#Ḥadīth #1)
Chapter 8 | What Allah (azwj) has Forbidden a Believer to do Against a Fellow Believer
171 - وعن زرارة قال: سمعت أبا عبد الله عليه السلام يقول: أقرب ما يكون العبد إلى الكفر أن يكون الرجل مواخيا للرجل على الدين، ثم يحفظ زلاته و عثراته ليضعه يوما ما.
171. It has been related that Zurarah said: I heard Abu 'Abd Allah saying: The closest stage to infidelity that one attains is that a person takes one to be his brother-in-faith then the latter keeps track of his mistakes and slips that he may use them against him someday.
Gradings are classical jarḥ-wa-taʿdīl, name-matched to a rijāl index (not individually re-verified).