Accuse your brother of something without proof...
Shaykh al’Fawzan حفظه الله quoted Imaam Muhammad bin ‘Abdul Wahhab:
“…You should not have dark suspicion concerning your muslim brother if you do not have any sound proof for what you suspect. To merely accuse your brother of something without proof is a major sin.”
(Sharh Kitaab al’Kabaair page 345)