Is a pilgrim in Ihram prohibited from cutting fingernails?
Chapter on What the Muhrim Must Avoid and What is Permissible for Him
Al-Mughni
Book of Hajj
Primary text
A pilgrim in Ihram is prohibited from cutting fingernails because nail cutting involves removing a part from which one benefits through refinement, which is forbidden, similar to hair removal. If a nail breaks, it may be removed without expiation. The consensus among scholars whose opinions we know is that a pilgrim may remove a broken nail by himself, as the broken nail causes pain and harm, analogous to hair growing into the eye or a predator attacking.
Supporting text
If more than the broken part is cut, expiation is due for the excess portion. If nail cutting is necessary to treat a sore, expiation is due. Ibn al-Qasim, the companion of Malik, held that no expiation is due in this case. If a nail is removed due to disease afflicting it, no expiation is due, as it is for curing the disease, similar to removal due to a break.