Whose kid is this

In the name of God
Whose kid is this
A man had two wives , both of them were pregnants and begot at the same time , one of them begot a son and the other a daughter , the woman who begot a daughter substituted her daughter with the son of other wife . The two wives claimed that the son is hers .
They went to Imam Ali to solve this problem , he brought two cups and asked the two women to fill the cup with her milk then he brought a balance to weigh the two cups . The woman whose her milk is heavy is the mother of the son and the other whose her milk is light is the mother of the daughter

Note : Imam is a term in Islam means a leader of people who doesn't think of doing any error (infallible

Imam Ali is a caliph of our prophet Mohammed