Some malls and butchers sell sacrificial animals before Eid ul Adha for a specific price and with specific characteristics in terms of weight and type of meat, but without specifying a particular animal. On the day of Eid, the person on whose behalf the sacrificial animal was slaughtered goes to collect it from the slaughterhouse. Is this sacrifice valid or not? On the other hand, when can the person who had appointed a charity to offer the sacrificial animal on his behalf get his hair cut and nails pared as he doesn`t know when the animal was slaughtered?