Musnad Abu Ya'la al-Mawsili 150:377

Narrated to us Mujahid ibn Musa, narrated to us Marwan ibn Mu'awiyah, narrated to us Abu 'Abd al-Malik al-Makki, narrated to us 'Abdullah ibn Abi Mulaykah, from 'Aishah, that the Prophet (peace be upon him) said: "The *usaylah* (honey-drop) is sexual intercourse."