When a messenger comes saying he has a message from God, offer him your hand and request him to shake hands with you. If he be an angel he will do so, and you will feel his hand. If he be the spirit of a just man made perfect ... Ask him to shake hands with you, but he will not move, because it is contrary to the order of heaven for a just man to deceive. If it be the devil as an angel of light, when you ask him to shake hands he will offer you his hand, and you will not feel anything; you may therefore detect him. Genesis 129:4