It is narrated from Sayyiduna Ibn Umar (may Allah be pleased with them both) that the Noble Prophet (peace and blessings be upon him) forbade the sale involving deception. Sayyiduna Ibn Umar (may Allah be pleased with them both) says that in the days of ignorance, people used to conduct transactions in such a way that they would give a she-camel and, in exchange, buy the unborn calf in the womb of a pregnant she-camel (and would say that when its calf is born, I will take it). The Noble Prophet (peace and blessings be upon him) forbade this.