It is reported that ʿAbdullāh b. Al-Mubārak – Allāh have mercy on him – said: “I borrowed a pen in the land of Syria, and it slipped my mind to return it to its owner. When I arrived in Marw, I looked and found it still with me, so I returned to the land of Syria and gave it back to its owner.” Tārīkh Baghdād (11/407)
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Related sayings.
What to do and not do when you see your brother has committed a sin.
A person of insight has deeper knowledge about some matters that others seem to feel safe from.