- If you do a favor for someone, forget it. --- إذا اتخذتم عند رجل يداً فانسوها

 If you do a favor for someone, forget it. This was said by one of the wise men of Arabia to his sons. Abu Ubaid said: He meant so that you would not feel indebted to people in your hearts, nor mention it with your tongues. He said: You spoil with reminders what you have done to ease your affairs; a generous person does not boast when he gives.

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The closest equivalent in English is:

Do a good deed and forget it.

Do good and then forget it.

Also:

Never remind people of the favors you did for them.

And a well-known proverb, very close in spirit, is:

Cast your bread upon the waters.

That is, do good without expecting anything in return or being reminded of it.

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قال بعض حكماء العرب لبنيه. قال أبو عبيد: أراد حتى لا يقع في أنفسكم الطول على الناس بالقلوب ولا تذكروها بالألسنة. قال:
أفسدت بالمن ما أصلحت من يسر*****ليس الكريم إذا أسدى بـمـنـان