It was narrated that Ibn 'Abbas (رضي الله عنه) said:

The Messenger of Allah (ﷺ) forbade ambiguous sales. Ayyoob said: Yahya explained ambiguous sales by saying Ambiguous sales include selling what the diver is going to bring up, selling a rebellious slave, selling a lost camel, selling what is in the wombs of an’am animals (camels, cows, sheep), selling metal that is still in its rock, selling what is in the udders, unless it is measured out.