Abu Ishaq al-Sabay'ai' أبو إسحاق السبيعي عمرو بن عبد الله · Chapters on Slaughtering

“Avoid those that are lactating.” (i.e. those from which milk is received).

“We asked the Messenger of Allah (ﷺ) about the fetus. He said: ‘Eat it if you wish, for it is considered legally slaughtered with the slaughtering of its mother.’”