Canonical Reference: Subhasita Sutta (Well-Spoken Words), Verse 451 Verified Source

“Speak only words that bring benefit, words that cause no remorse, words that bring joy to others. Speak truth and speak with kindness.”

Canonical Pali Original: Tameva vācaṃ bhāseyya, yāyattānaṃ na tāpaye; Pare ca na vihiṃseyya, sā ve bhāsitā subhāsitā.

— Gautam Buddha
The Awakened One, Founder of Dhamma
Historical Setting & Context:

Delivered at Jetavana in Savatthi, setting forth the four hallmarks of Right Speech (Sammā Vācā).