It was narrated that 'Aishah the wife of the Prophet said: When the two circumcised parts meet, then bath is obligatory. The Messenger of Allah and I did that, and we bathed.
Ubayy bin Ka'b said: That was a concession that was granted in the early days of Islam, then we were commanded to have a bathe after that.
It was narrated from Abu Hurairah that: The Messenger of Allah said: When a man sits between the four parts (arms and legs of his wife) and has intercourse, then bath is obligatory.
It was narrated from 'Amr bin Shu'aib from his father, that his grandfather said: The Messenger of Allah said: 'When the two circumcised parts meet, and (the tip of the penis) disappears, then bath is obligatory.'