That myth largely originated when Paul proposed ending all foreign aid in his first budget plan. Foreign aid is something he philosophically opposes.
As usual, the media was responsible for changing the narrative. Instead of reporting that Paul wanted to end all foreign aid, they wrote headlines that indicated he specifically targeted Israel for cuts. That never happened. Paul has since modified his approach, focusing on first ending aid to countries that hate us.
There is also the wrong assumption that Israel would be hurt if foreign aid was cut off. In fact, it would make Israel stronger. That is what Benjamin Netanyahu once told the U.S. Congress:
Here is the truth: Rand Paul is a strong supporter of Israel. He has stated that an attack on Israel would be treated as an attack on the U.S.
If that doesn't satisfy concerns about Paul's position on Israel, nothing will.