Sahih Muslim 1464
Sahih Muslim · Book 17: The Book of Suckling · It is permissible for a wife to give her turn to a co-wife
Hisham reported on the authority of his father that 'A'isha (Allah be pleased with her) used to say:
وَحَدَّثَنَاهُ أَبُو بَكْرِ بْنُ أَبِي شَيْبَةَ ، حَدَّثَنَا عَبْدَةُ بْنُ سُلَيْمَانَ ، عَنْ هِشَامٍ ، عَنْ أَبِيهِ ، عَنْ عَائِشَةَ ، أَنَّهَا كَانَتْ تَقُولُ أَمَا تَسْتَحْيِي امْرَأَةٌ تَهَبُ نَفْسَهَا لِرَجُلٍ حَتَّى أَنْزَلَ اللَّهُ عَزَّ وَجَلَّ { تُرْجِي مَنْ تَشَاءُ مِنْهُنَّ وَتُؤْوِي إِلَيْكَ مَنْ تَشَاءُ} فَقُلْتُ إِنَّ رَبَّكَ لَيُسَارِعُ لَكَ فِي هَوَاكَ.
Does the woman not feel shy of offering herself to a man? Then Allah the Exalted and Glorious revealed this verse:" You may defer any of them you wish and take to yourself any you wish." I ('A'isha said): It seems to me that your Lord hastens to satisfy your desire.