The Messenger of Allah ﷺ was asked about ghilah, the practice of a husband having intercourse with his wife while she is nursing. He replied, "If it were harmful to anyone, it would have harmed the Persians and the Romans."
أن رسول الله ﷺ سئل عن الغيل فقال: لو كان ضارا أحدا ضر فارس والروم.
Bazzar narrated it in Kashf Astar (1454) from Muhammad bin Abu Ghalib, who said, Safwan bin Salih told us, who said, Isa bin Yunus told us, who said, Ibn Jurayj told us, from Ata, from Abdullah bin Abbas, and he related it.Haythami said in Majma (4/298), "Its narrators are the narrators of sahih." I say, it is as he said. Ibn Jurayj is a mudallis and he did use the ambiguous form of narration, but his ambiguous narration from Ata bin Abu Rabah is presumed to be direct hearing, due to how closely he accompanied him.On this subject there is also what was narrated from Asma bint Yazid bin Sakan, who was his freedwoman, that she heard the Messenger of Allah ﷺ say, "Do not kill your children secretly, for by the One in whose hand is my soul, having intercourse with a nursing wife can overtake the horseman on the back of his horse until it throws him down."Abu Dawud (3881), Ibn Majah (2021), and Ahmad (27562) narrated it, and Ibn Hibban (5984) graded it sahih, all of them through the hadith of Muhajir bin Abu Muslim, narrating from Asma bint Yazid, who related it. The wording given here is Ibn Majah's, while the wording of Abu Dawud and Ibn Hibban is, "Do not kill your children secretly, for having intercourse with a nursing wife overtakes the horseman and throws him off his horse."In the chain is Muhajir bin Abu Muslim, whom no one deemed reliable except Ibn Hibban. For this reason Hafiz said in Taqrib, "acceptable," meaning when corroborated, and since he was not corroborated, he is weak in hadith.Moreover, its wording contains an objectionable element, given what was established as sahih regarding the permissibility of intercourse with a nursing wife in the preceding hadith, and it also contradicts what is observed by the senses, except in special cases.