Is there strict prohibition from cutting nails and hair for those who would like to perform the qurban or sacrifice.
From the Islamic Religious Council of Singapore Website (MUIS) :
Scholars differ on this issue. The differences can be classified as follow:
Sa’id bin Al Musayyib, Rabi’ah, Imam Ahmad, Ishaq and Dawud are of the opinion that the ruling to cut the hair and nails for those who are planning to perform the qurban or the sacrifice, is haraam, until the qurban has been carried out.
This is the opinion of the Shafi’i school of thought. This opinion states that going against the prohibition is makruh (makruh tanzih) or disliked, and not haraam.
This opinion is derived from the hadith of ‘Ayesha (r) who said that there were times when the Prophet(s) had performed the qurban (but he was not in ihram/performing hajj), and yet he did not prohibit what Allah has made permissible, until he had sacrificed the hadi (his qurban in Makkah). In other words, although the Prophet (s) was going to perform the qurban, but because he was not in ihram, he did not do as how those in ihram had to do. Hence, it is understood to mean that he did not observe the prohibition of cutting his hair and nails like how a person in ihram would have to.
This is the opinion of Imam Abu Hanifah and Imam Malik who said that it is not even makruh at all.
And Allah knows best.