Is it correct that one shouldn’t clip one’s nails and cut hair if one is to sacrifice animal on the tenth of Dhul Hajj or later? Why? It seems not consistent with teachings of a religion which emphasizes on cleanliness.
The practice of refraining from clipping nails and cutting hair by those who intend to sacrifice animal was introduced by the prophet alaihissalam (Muslim, 5121). It has been a part of the old tradition of sacrifice. The idea is to remain in a proper frame of mind of sacrificing everything whatever it takes to please God before doing the ritual of animal sacrifice. Islam doesn’t allow believers to resort to asceticism. However, there are a few exceptions where we have been asked to go against the normal routine to develop special feelings of closeness to the Almighty. One can call it a very limited, controlled asceticism. The other examples similar to it are fasting, itikaf, Hajj, Umrah, ihram etc.