Sahih Muslim | Book 8 | Hadith Number 3394

Narrated by Sa'd b. Abu Waqqas (Allah be pleased with him)
Sa'd b. Abu Waqqas (Allah be pleased with him) reported that a person came to Allah's Messenger (may peace be upon him) and said: I do 'azi with my wife. Thereupon Allah's Messenger (may peace be upon him) 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.