Answer
Wa `alaykum As-Salamu waRahmatullahi wa Barakatuh.
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.
Dear questioner, we would like to thank you for the great confidence you place in us, and we implore Allah Almighty to help us serve His cause and render our work for His Sake.
A male pilgrim is allowed to wear diapers if needed.
In his response to your question, Sheikh Ahmad Kutty, a Senior Lecturer and an Islamic Scholar at the Islamic Institute of Toronto, Ontario, Canada, states:
Ihram for males consists of two unsewn pieces of cloth. However, you are allowed to wear a diaper that is not sewn if needed – for health reasons. If you are forced to wear stitched ones, then, as per the ruling of the majority, you need to expiate for it: expiation involves fasting three days or feeding six poor persons, or offering a sacrifice.
There is another view on this. There are reports from `A’ishah, the beloved wife of the Prophet (peace be upon him) that she allowed the workers (accompanying her in hajj) to wear undergarments as their ihram garbs were too short and hence their private parts exposed when they were performing their chores. In another report, we read that the eminent companion `Ammar ibn Yasir used to wear an undergarment as he was suffering from bladder incontinence.
It is best to follow the rule of the majority as it is the safest unless you are wearing an ordinary diaper which is unsewn. Hence, the question of expiation does not arise at all.
Allah Almighty knows best.