Praise be to Allah,
Hushaym narrated to us from Humayd from Anas ibn Maalik who said that the Prophet (peace and blessings be on him) would visit all of his wives in one single night and perform only one ghusl”.
(Musnad Ahmad, Vol. 3, p. 98. The isnaad of this h.adeeth is Saheeh according to the conditions set by al-Bukhaaree and Muslim.)
Commentary
Ghusl refers to the full ablution or washing of the whole body that a Muslim must perform after having sexual intercourse with one’s spouse or any discharge of semen while awake or asleep in a wet dream.
Source:
Thulaathiyyaat Musnad Ahmad ibn Hanbal (may Allah have mercy on him)
Reports of Imaam Ahmad that have only three narrators between him and the Prophet, peace, and blessings be upon him.
Shaykh Muhammad ibn Ahmad ibn Saalim as–Saffaareenee al–Hanbalee ~(1114 –1188 AH)