Midrash sur Chroniques 2 5:2

And all his sons and all his daughters rose (Genesis 37:35) - How many daughters did he have? Only one, and probably she was buried. Rather, this teaches that a person never stops calling their son-in-law "my son" and their daughter-in-law "my daughter". Rabbi Yehudah says: the brothers married [twin] sisters [that were born with them], as it is written "And all his sons and all his daughters rose to console him". "But he refused to be consoled" - a Roman matron asked Rabbi Yosi: it is written "Yehuda became more powerful than his brothers" (II Chron. 5:2) and it is written "when Yehuda was comforted he went to shear his sheep" (Genesis 38:12) and this father, of all of them, refuses to be comforted!? He answered: it is possible to be comforted for those who died, but it is not possible to be comforted for those alive. "And his father cried over him" - this is Itzchak. Both Rabbi Levi and Rabbi Simon say: he would cry at his father's house, and once he left he went and bathed and oiled his skin, and ate and drank. And why did not Itzchak reveal this [that he was alive] to him? Itzchak said: if the Holy One of Blessing did not reveal, I am not revealing. Rabbi Simon said: this is because everyone who one mourns for, one mourns with.