Musnad Abi Ya'la 4926 — in a gathering of learning in which I too was

It is narrated from Sayyiduna Abu Hurayrah (may Allah be pleased with him) that in a gathering of learning in which I too was present, the things that make the ritual bath (ghusl) obligatory were discussed. Some people said: "When a man has intercourse (with a woman)," and some said: "(Ghusl is not obligatory) until the water (semen) is emitted." (Sayyiduna Abu Hurayrah (may Allah be pleased with him) said:) I said: "I will bring you certain knowledge of this." Then I went to the Mother of the Believers, Sayyidah Aishah (may Allah be pleased with her), and said to her: "O Mother of the Believers! I want to ask you about a matter, but I feel shy to ask you about it." She said: "Do not be shy to ask me about what you could ask your own mother, for I am indeed your mother." I said: "O my mother! What makes the ritual bath obligatory?" She said: "You have come to the right and well-informed person. When the man sits between her four limbs (arms and legs) and the two circumcised parts meet, the ritual bath has certainly become obligatory."