Abu Asma' al-Rahabi relates that Sayyiduna Thawban (may Allah be pleased with him), the mawla of the Messenger of Allah (peace and blessings be upon him), told him: I was standing before the Messenger of Allah (peace and blessings be upon him) when one of the rabbis of the Jews came and said: Peace be upon you, O Muhammad. I pushed him so hard that he nearly fell. He asked: Why did you push me? I said: Why did you not say, 'O Messenger of Allah'? The Jew said: We call him only by the name his family gave him. So the Messenger of Allah (peace and blessings be upon him) said: "Indeed, my name which my family gave me is Muhammad (peace and blessings be upon him)." The Jew said: I have come to ask you something. The Messenger of Allah (peace and blessings be upon him) said: "Will it benefit you if I tell you?" He said: I will hear (the answer) with my own ears. He (peace and blessings be upon him) had a stick with him, with which he (peace and blessings be upon him) began scratching the ground, and he said: "Ask." The Jew said: On the Day when "the earth will be changed into another earth, and so will the heavens" [Surah Ibrahim: 48] , where will the people be? The Messenger of Allah (peace and blessings be upon him) said: "They will be in darkness, short of the Bridge (al-Sirat)." He asked: Who will be the first to cross it? He (peace and blessings be upon him) said: "The poor among the Muhajirun." He asked: When they enter Paradise, what will their first hospitality be? He (peace and blessings be upon him) said: "The lobe of the liver of the fish." He asked: What will their meal be right after that? He (peace and blessings be upon him) said: "The bull of Paradise, which used to graze on its outskirts, will be slaughtered for them." He asked: And what will their drink be with it? He (peace and blessings be upon him) said: "From a river of Paradise named Salsabil." He said: You have spoken the truth. Then he said: I have come to ask you about something that no one on the face of the earth knows except a prophet, or one or two men. He (peace and blessings be upon him) said: "Will it benefit you if I tell you?" He said: I will listen to it attentively. He said: I have come to ask you about the child (and how it is formed). He (peace and blessings be upon him) said: "The man's fluid is white and the woman's fluid is yellow. When the two come together and the man's fluid prevails over the woman's fluid, a boy is born by the permission of Allah; and when the woman's fluid prevails over the man's fluid, a girl is born by the permission of Allah." The Jew said: You have spoken the truth, and you are indeed a Prophet of Allah. Then he turned and left, and the Messenger of Allah (peace and blessings be upon him) said: "This man asked me about the things he asked me about, and I had no knowledge of any of them until Allah Almighty granted me that knowledge." This hadith is sahih (authentic) on the condition of the two Shaykhs (Bukhari and Muslim), but they did not record it.