Sayyiduna Abdullah bin Abbas (may Allah be pleased with them both) says: The Jews came to the Prophet Muhammad (peace and blessings be upon him) and said: O Abul Qasim! We want to ask you about some things; if you give (correct) answers, we will follow you, affirm you, and believe in you. The Prophet (peace and blessings be upon him) took from them the covenant and pledge that Israel (Yaqub, peace be upon him) had taken for himself. They said: Whatever we say, Allah Almighty is a witness and guardian over it. (The series of questions begins.) They said: Tell us about the sign of a Prophet. The Prophet (peace and blessings be upon him) said: "The eyes of a Prophet sleep, but his heart does not sleep." They said: How are males and females produced from a woman's womb? The Prophet (peace and blessings be upon him) said: "The (male and female) fluids mix; if the woman's fluid prevails over the man's fluid, a female is born, and if the man's fluid prevails over the woman's, a male is born." They said: Tell us about "Ra’d" (the thunder or rumbling of clouds), what is it? The Prophet (peace and blessings be upon him) said: "Ra’d is the name of an angel; the affairs of the clouds are entrusted to him. In his hands is a sword (or whip) of fire, with which he drives the clouds here and there, and when he moves the clouds (by scolding or commanding them in a specific manner), then the sound is produced which (we) hear, until he brings them to the place he is commanded to."