This meme has floated around the internet for years. It is absolutely and completely unfounded. These charges are spurious. There is not the slightest evidence from the first centuries to support this rumor. No responsible Jewish person would spread the completely unsubstantiated charge. The best thing to do with this false rumor is to not even discuss it because when we do, we give legs to this false claim. However, you asked, so I need to respond.
The evidence is that this rumor was begun by the Greek philosopher and enemy of Christianity, Celsus, in the mid-second century. He wrote a polemic against Christianity, loaded with false accusations about Jesus and his followers. He called Jesus the son of Pentera, implying that Mary was raped by a Roman soldier. Pentera was a very common soldier’s name in the Roman army at that time, so this completely unsubstantiated rumor was that a generic, unidentified Roman soldier raped Mary. It would be like saying “Joe” did it. Of course, Celsus cannot identify this supposed soldier. The tomb of a Roman soldier named Pentera was discovered in Germany in 1859, which gave extra fuel to this bogus fire, but, again, there is no reason whatsoever to accept this as evidence. The fact that there was a soldier in Syria at that time named Pentera is like saying there was a soldier named Joe in Italy during World War II.
This fabricated rumor of Celsus was picked up in the Toledot Yeshu, an even more irresponsible fabricated Jewish polemic against Jesus in the Middle Ages. The outrageous false claims about Jesus in this unfortunate document do not bear mentioning. The fact that Toledot Yeshu picked up this false rumor is further evidence against, not for, the false rumor about the parentage of Jesus.
Who would know who the father of Mary was? Would a Greek philosopher writing 150 years later be likely to know what happened to Mary? Is this believable? The people who would know are Joseph and Mary. His mother and adoptive father would know whether Mary was raped. Mary said she was not raped. Joseph trusted her and married her. Apparently, Jesus’ contemporaries did not believe he was raped.
Besides, Jesus walked on water, changed water to wine, calmed the storm, healed the blind, the lame and the deaf, raised more than one person from the dead and was, himself, raised from the dead on the third day. This is more than enough reason to believe that Jesus had divine origins, as he himself claimed.
This despicable rumor ought not to be passed along by any self-respecting person. You should go back to this Jewish person and scold him for passing along such spurious false rumors. He should be ashamed of such behavior.