The third sutta of the Mahā Vagga of the Suttanipāta. The Buddha tells the monks that good speech is that which is spoken well, righteously, affectionately, and truthfully. Vaṅgīsa Thera, who is present, renders the Buddha’s speech into verse. SN.78 f.
The sutta is repeated in the Saṃyuttanikāya. S.i.188.