مِشْكَاةُ الْمَصَابِيحِ
Mishkat al-Masabih 455
Purification
Associating with one who is defiled, and what is permitted - Section 1
وَعَنْ أَنَسٍ قَالَ: كَانَ النَّبِيُّ صَلَّى اللَّهُ عَلَيْهِ وَسَلَّمَ يطوف على نِسَائِهِ وَبِغسْلِ وَاحِد. رَوَاهُ مُسلم
Anas said that the Prophet (ﷺ) used to have intercourse with his wives, with only a single washing. Muslim transmitted it.
Mishkat al-Masabih, 455صَحِيح (الألباني)