It is narrated from Sayyiduna Abu Sa'id (may Allah be pleased with him) that the Prophet Muhammad (peace and blessings be upon him) said: "When any one of you comes to his wife (has intercourse with her) and then intends to do so again, he should perform ablution." This is the narration of San‘ani. The rest of the narrators, when narrating from Abu Mutawakkil, have mentioned « عن » instead of « سمعت ».