What should a person who wants to sacrifice refrain from doing? 

قال رسول الله(ﷺ):إِذَا رَأَيْتُمْ هِلاَلَ ذِي الْحِجَّةِ وَأَرَادَ أَحَدُكُمْ أَنْ يُضَحِّيَ فَلْيُمْسِكْ عَنْ شَعْرِهِ وَأَظْفَارِهِ ‏"‏. صحيح مسلم 

Umm Salama reported (these words) directly from Allah's Messenger (ﷺ):

If anyone has in his possession a sacrificial animal to offer as a sacrifice (on 'Id al-Adha), he should not get his hair cut and nails trimmed after he has entered the first days of Dhu'l Hijja.

  Sahih Muslim 

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So whoever wants to sacrifice, he must not take anything from his hair, nails or skin, from the first day of the month of Dhu al-Hijjah, until after he slaughtered his sacrifice, on yaum al- nahr (the day of sacrifice), which is the first day of the blessed Eid al-Adha.