Answer
In the Name of Allah, Most Gracious, Most Merciful.
All praise and thanks are due to Allah, and peace and blessings be upon His Messenger.
In this fatwa:
There is no objection to a married couple in bathing together while fasting, they certainly may not do so while they are nude.
Responding to your question, Sheikh Ahmad Kutty, a senior lecturer and an Islamic scholar at the Islamic Institute of Toronto, Ontario, Canada, states:
There is no objection to a married couple in bathing together while fasting, they certainly may not do so while they are nude.
While fasting, we are to stay away from any activities that may directly or indirectly lead to nullifying our fasts.
Fasting properly involves not just abstaining from food, drink, and sexual activities, but also restraining our ears, eyes, tongues, and thoughts.
It is quite easy for the couple who bathes together while nude to become aroused and do things that may break the fast. The Prophet (peace be upon him) told us in clear terms to stay away from dubious things, for, by doing so, we are better able to safeguard our faith and honor.
Therefore, you are best advised to stay away from such activities while fasting, keeping in mind that you are free to partake in them at night.
Almighty Allah knows best.