It is more preferable for a Muslim to slaughter the animal of his Qurbani with his own hands. However, if he is unable to slaughter the animal himself, or does not want to do so for some reason, he can request another person to slaughter it on his behalf. In this case also, it is more preferable that he, at least, be present at the time of slaughter.
However, his absence at the time of slaughter does not render the Qurbani invalid, if he has authorized the person who slaughtered the animal on his behalf. It is a Sunnah to lay the animal with its face towards the Qiblah, and to recite the following verse of the Holy Quran:
I, being upright, turn my face towards the One who has created the heavens and the earth, and I am not among those who associate partners with Allah. ( Al-An'am, 6:79)
