From Sahih Muslim (Hadith 3567):
Sa'd b. Abu Waqqas (Allah be pleased with him) reported that a person came to Allah's Messenger (ﷺ) and said: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
Reference: Muslim 3567