I was about to forbid sexual intercourse during the breastfeeding period until I considered that the Romans and the Persians do it without any harm done to their children thereby

This Hadīth shows that the Prophet (may Allah's peace and blessings be upon him) wanted to forbid having intimate relations with one's wife during the suckling period, for it was common among the Arabs that doing so would cause harm to the baby. However, he did not forbid it once he came to know for sure that some peoples, like the Persians and the Romans, reported that no harm was caused to their children on account of doing this.

The Prophet (may Allah's peace and blessings be upon him) was asked about ejaculating outside the vagina. He likened this to a pre-Islamic practice, when the Arabs used to bury their girls alive. The difference between both practices is that the infanticide was done openly, yet coitus interruptus is done privately.