I heard Allah's Messenger (ﷺ) saying this. The rest of the hadith is the same concerning 'azl and ghila (cohabitating with a suckling woman), but with a slight variation of words.
Sahih Muslim Book 16, Hadith 168
← Previous Hadith I went to Allah's Messenger (ﷺ) along with some persons and he was saying: I intended to prohibit cohabitation with the suckling women, but I considered the Greeks and Persians, and saw that they suckle their children and this thing (cohabitation) does not do any harm to them (to the suckling women). Then they asked him about 'azl, whereupon he said. That is the secret (way of) burying alive, and Ubaidullah has made this addition in the hadith transmitted by al-Muqri and that is:" When the one buried alive is asked."

Sahih Muslim Book 16, Hadith 167 Next Hadith → I do 'azi with my wife. Thereupon Allah's Messenger (ﷺ) said: Why do you do that? The person said: I fear harm to her child or her children. Thereupon Allah's Messenger (way peace be upon him) said: If that were harmful it would harm the Persians and the Greeks.

Sahih Muslim Book 16, Hadith 169