The details of this account are taken from the Quran.
There is a man who wrote the biography of Mohammed. His name is Ebn Hisham. He is well known by the name of Abed EL Malak Bin Hisham. And he wrote the biography of Mohammed. And in his biography he mentions that when Mohammed was at the cave of Hira, outside of Mecca, he was alone, when a spirit came and squeezed him, and told him, “Read.” He went to this wife scared. And he continued to be in doubt of what happened to him. And one day, his wife Khadijah said to him, “Mohammed, let us put that on a test. When the spirit comes to you, tell me, and we will test if that spirit is really Gabriel the angel, or a bad spirit.” He said OK. One day, he was sitting with her, and he said, “Khadijah, the spirit came!” She said, “Come, and sit on my right side.” So, he sat on her right side. She said, “Mohammed, do you see the spirit?” He said, “Yes.” She said, “Then sit on my left side.” So, he switched and he sat on her left side. “Do you see the spirit?”Khadijah asked. “Yes,” Mohammed answered. “Then sit on my lap.” He sits on her lap. “Do you still see the spirit?” “Yes,” Mohammed answered. Then she uncovered herself to show some of her feminine parts of body. And then she said, “Do you see the spirit?” He said, “No.” She said, “That spirit is good because he doesn’t want to see my feminine part. You are the prophet of God.” And by that he came to be convinced that that spirit who was talking to him was the angel Gabriel, and a good spirit, because when he saw his wife almost naked, he didn’t stay to see. And for me, this is a very strange way to test a spirit. by Dr. Labib