He saw the wagons that Yosef sent. (Bereishis 45:27)
He gave them a sign about the subject he was occupied with when he left him – the passage of eglah arufah. Thus it says, “He saw the wagons that Yosef sent,” and does not say, “that Pharaoh sent.” (Rashi)
There once was an agunah whose husband had left her many years before and disappeared. One day, a man showed up, claiming he was her husband. To prove his claim he showed that he knew all about everything connected to the home. The Vilna Gaon instructed them to ask him about his seat in the shul. Because if he is lying, and he procured the information from the husband in order to steal his wife, he would not have asked the husband about kedushah matters at all.
And so it was. He did not know where his seat was in the shul, and his evil scheme was revealed.
When great tzaddikim have a question about a certain matter, they often search in the Torah for an indication, because everything is in the Torah. It is possible that the Vilna Gaon found an indication here, in our parshah, for the instructions he gave. Yaakov was looking for a sign whether the viceroy in Egypt was really Yosef as claimed. Yaakov didn’t believe it until he received a sign about a kedushah matter, which was that they had learned the subject of eglah arufah together.
