لسانك لا تذكر به عورة امرئ * فكلّـك عورات وللناس ألسـنوعينك إن أبدت إليك معايباً * فدعها وقل : يا عين للناس أعينُ

"Do not use your tongue to mention the faults of others,
for you are full of faults and other people have tongues, too.
And if your eye reveals to you others' defects, tell it,
'O eye of mine, they have eyes too.'"

-Imam Shafi'i

من نمّ لك نمّ عليكومن نقل اليك نقل عنك

Whoever shares slander with you will slander about you;
And whoever reports to you will soon report about you.

-Imam Shafi'i

(A similar version to the above quote, that means basically, "Whoever gossips with you gossips about you!")

طعن اللسان أنفذ من طعن السنان وجرح الكلام أصعب من وقع السهام

"The stab of the tongue penetrates more than the stab of the spear, and the wounds from words are more difficult than those from the arrow."

من اغتاب خرقومن استغفر رقع

"He who slanders tears and rips away,
and he who asks forgiveness patches."

يــابنيَّ أتقوا الجواب، وزلة اللســان، فإني وجدت الرجل تعثر قدمه فيقوم من زلَّته وينتعش منها سوياً، ويزل لسانه فيوبقه، ويكون فيه هلكته

"My son, be wary of one's reply and the slip of one's tongue. For I have found that a man's foot may slip, but he can stand up and recover from it, while a slip of his tongue will lead to his destruction."

-Abdullah b. Saddad