Surah Al-Ahzab (The Enemy Alliance), Verse 52

لَا یَحِلُّ لَكَ النِّسَآءُ مِنْ بَعْدُ وَلَاۤ اَنْ تَبَدَّلَ بِهِنَّ مِنْ اَزْوَاجٍ وَّلَوْ اَعْجَبَكَ حُسْنُهُنَّ اِلَّا مَا مَلَكَتْ یَمِیْنُكَ وَكَانَ اللّٰهُ عَلٰی كُلِّ شَیْءٍ رَّقِیْبًا 

Laa yahillu lakan nisaaa'u mim ba'du wa laaa an tabaddala bihinna min azwaajinw wa law ajabaka husnuhunna illaa maa malakat yameenukk; wa kaanal laahu 'alaa kulli shai'ir Raqeeba

“It is not lawful for thee (to marry more) women after this, nor to change them for (other) wives, even though their beauty attract thee, except any thy right hand should possess (as handmaidens): and Allah doth watch over all things.”

Quran 33:52 (Yusuf Ali Translation)