Musannaf Ibn Abi Shayba 1:870

Ibn ‘Ulayyah narrated to us, from al-Taymi, from Abu ‘Uthman, from Salman ibn Rabi‘ah, who said: ‘Umar said to me, “O Salman, when you come to your wife, then you wish to return [to her], what do you do?” He said: I said, “What should I do?” He said, “Perform ablution (wudu) between them, an ablution.”