He whose speech is unwholesome cuts himself with his axe. When a person praises someone who should be blamed, or attacks someone worthy of praise, then this man is accumulating evil with his mouth and this evil will not lead to happiness.
It is little harm if one loses money in gambling with dice, even losing everything, including oneself; but if one bears ill-will towards well-conducted ones it is greater harm indeed.
Insulting men of real worth, bearing ill-will in thought and speech, leads to aeons upon aeons in the states of misery.
The Messenger of God... took hold of his tongue and said, "Restrain this". I said, "O Prophet of God, will what we say be held against us?" He said, "Is there anything that topples people on their faces into hell-fire other than the harvests of their tongues?"
Hadith of an-Nawawi
The tongue is an unrighteous world among our members, staining the whole body, setting on fire the cycle of nature, and set on fire by hell. For every kind of beast and bird, of reptile and sea creature, can be tamed and has been tamed by humankind, but no human being can tame the tongue — a restless evil, full of deadly poison.
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