Cutting nails is the Sunnah of the Holy Prophet (sws).
This practice relates to that type of Islamic directives and practices which
have been promulgated to ensure purification of the physical self of a believer.
Since the basic purpose of Islam is inner purification, it lays great stress on
physical purification as well because the latter cultivates a sense of purity
and ultimately helps in attaining the purification of the inner self. Therefore,
we see that many practices have been instituted for the purpose, for example,
shaving off the hair from under the armpits and from the pubic area. One must
not ignore these important Sunnan. However, there exists a categorization among
the Sunnan in terms of their binding nature. For instance, we, as Muslims, do
not condone that anyone should not circumcise any of his male offspring though
we will not be much bothered if this particular person does not greet us in the
ceremonial way by saying Assālāmu ‘alaykum. The Sunnah of cutting nails belongs
to this second type as is the ceremonial greeting.
You should therefore keep trying to convince your husband, of
course, very politely and ask him to give due importance to the practice. If
however he does not listen, you may comply with his wishes as far as this
practice of cutting nails is concerned. Allah will surely not hold you
responsible as long as it is not your desire to transgress. And do not forget to
pray to the Almighty that He may give you wisdom to persuade him and that He may
instil within your husband a close attachment to the religion.