Imam al-Shafi'i (may Allah have mercy on him) said: "A hadith has been narrated about this, even though it is among those reports whose like is not established."
Sayyiduna Abu Sa'id (may Allah be pleased with him) said that the Messenger of Allah (peace and blessings be upon him) said: "When one of you comes to his wife and then wishes to return (to her), let him perform ablution."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب النكاح / 14087