This was said by the Buddha, the Perfected One: that is what I heard. Vuttañhetaṁ bhagavatā vuttamarahatāti me sutaṁ:

“One thing, mendicants, arises in the world for the detriment and suffering of the people, against the people, for the harm, detriment, and suffering of gods and humans. “Ekadhammo, bhikkhave, loke uppajjamāno uppajjati bahujanāhitāya bahujanāsukhāya bahuno janassa anatthāya ahitāya dukkhāya devamanussānaṁ. What one thing? Katamo ekadhammo? Schism in the Saṅgha. Saṅghabhedo. When the Saṅgha is split, they argue, insult, block, and forsake each other. Saṅghe kho pana, bhikkhave, bhinne aññamaññaṁ bhaṇḍanāni ceva honti, aññamaññaṁ paribhāsā ca honti, aññamaññaṁ parikkhepā ca honti, aññamaññaṁ pariccajanā ca honti. This doesn’t inspire confidence in those without it, and it causes some with confidence to change their minds.” Tattha appasannā ceva nappasīdanti, pasannānañca ekaccānaṁ aññathattaṁ hotī”ti.

The Buddha spoke this matter. Etamatthaṁ bhagavā avoca. On this it is said: Tatthetaṁ iti vuccati:

“A schismatic remains for the eon “Āpāyiko nerayiko, in a place of loss, in hell. Kappaṭṭho saṅghabhedako; Taking a stand against the teaching, Vaggārāmo adhammaṭṭho, favoring factions, they ruin their sanctuary. Yogakkhemā padhaṁsati; After causing schism in a harmonious Saṅgha, Saṅghaṁ samaggaṁ bhetvāna, they burn in hell for an eon.” Kappaṁ nirayamhi paccatī”ti.

This too is a matter that was spoken by the Blessed One: that is what I heard. Ayampi attho vutto bhagavatā, iti me sutanti.