“Reckless words pierce like a sword, but the tongue of the wise brings healing” (Prov. 12:18).

“He who guards his lips guards his soul, but he who speaks rashly will come to ruin” (Prov. 13:3).

“A man of knowledge uses words with restraint, and a man of understanding is even-tempered. Even a fool is thought wise if he keeps silent, and discerning if he holds his tongue” (Prov. 17:27-28).

“Do you see a man who speaks in haste? There is more hope for a fool than for him” (Prov. 29:20).

NB:  power of words depends on the character of the speaker:

“The mouth of the righteous is a fountain of life, but violence overwhelms the mouth of the wicked” (Prov. 10:11).

“The tongue of the righteous is choice silver, but the heart of the wicked is of little value” (Prov. 10:20).

“The tongue that brings healing is a tree of life, but a deceitful tongue crushes the spirit” (Prov. 15:4).

“The tongue has the power of life and death, and those who love it will eat its fruit” (Prov.. 18:21).

wisdom of Saadi:

“Soft speech acts like water on the fires of wrath” (Saadi, Bostan, chap. 4). ”

Those who reflect upon right and wrong are better than triflers with ready answers” (Saadi, Bostan, chap. 7).

“Prepare to speak only when thy words are likely to have an effect” (Saadi, Golestan, chap. 8).

“Whoever gives advice to a self-willed man stands himself in need of advice” (Saadi, Golestan, chap. 8).