Musnad Ahmad

It is narrated from Sayyiduna Ibn Abbas (may Allah be pleased with them both) that the Prophet (peace and blessings be upon him) forbade deceptive sales and trade. The narrator of the hadith, Ayyub, says that Yahya explained deceptive trade by stating that it also includes the case where a person says, "I am casting a net in the river; whatever fish come into it, I sell them to you for such and such amount," and the sale of a runaway slave, the sale of a wild goat that is prone to escape, the sale of the unborn offspring of animals, the sale of the earth from mines, and the sale of the milk present in the udders of an animal without measuring it. However, if the milk is measured and then sold, it is permissible.