Is it necessary to purchase the whole aqiqah (sacrificial animal) and have it slaughtered by the butcher, or is it permissible for the butcher to slaughter it with the intention of aqiqah and then weigh the net meat after slaughter?

The Aqiqah is an animal slaughtered for a newborn, in gratitude to Allah for His blessing. It is a confirmed Sunnah: two sheep for a boy and one sheep for a girl. The conditions applicable to the sacrificial animal for Eid al-Adha are also sufficient for the Aqiqah. It is preferable to slaughter it on the seventh day, otherwise on the fourteenth, or failing that, on the twenty-first. It is permissible to slaughter it at any time thereafter, and there is no sin in delaying it. Only slaughtering is sufficient for it.