Hadith Q221
إِذِ الْمُتَوَضِّئُ بَعْدَ الْجِمَاعِ يَكُونُ أَنْشَطُ لِلْعَوْدَةِ إِلَى الْجِمَاعِ، لَا أَنَّ الْوُضُوءَ بَيْنَ الْجِمَاعَيْنِ وَاجِبٌ، وَلَا أَنَّ الْجِمَاعَ قَبْلَ الْوُضُوءِ وَبَعْدَ الْجِمَاعِ الْأَوَّلِ مَحْظُورٌ.
Because performing ablution after intercourse refreshes a person for intercourse again, not because it is obligatory to perform ablution between two acts of intercourse, nor because it is prohibited or unlawful to have intercourse again before performing ablution after the first intercourse.
Hadith 221
Sayyiduna Abu Sa'id (may Allah be pleased with him) narrates from the Noble Prophet (peace and blessings be upon him) that he said: "When any one of you intends to have intercourse again, he should perform ablution, for it will bring vigor and readiness for him to have intercourse again."