After Prophet (PBUH) fled Mecca, his enemies went after him. So, he, and his closest companion Abu Bakr RA, hid in a cave. He enemies reached the opening of the cave, but the enemies did not enter the cave because they noticed a spider’s web covering the opening of the cave, so they thought that it was impossible for Mohammad PBUH to have entered that cave. This miracle is mentioned in the Quran.
Due to this, some scholars say that we should not kill spiders.
