Praise be to Allah.
What is prescribed when a child is born is for the family to slaughter the ‘aqeeqah on his behalf, on the seventh day. Two sheep should be slaughtered for a boy and one for a girl. The family can distribute the meat or part of it, or they can cook it or some of it and distribute it to family, relatives and neighbours.
If the family is unable to slaughter the ‘aqeeqah on the seventh day, then they may do so on the fourteenth, if they cannot do that then on the twenty-first, and if they cannot do that then on whatever day they can after that.
See the rulings on ‘aqeeqah in the answer to question no. 20018. It is permissible to distribute the meat of the ‘aqeeqah raw or cooked, as it says in the answer to questions no. 26046, 8423 and 8388.
The fortieth day after birth or death is of no significance; this is a Pharaonic custom and it is not permissible for the Muslim to seek out this day for anything that has to do with worship.
In the answer to question no. 12552 we have quoted the comments of Shaykh Ibn Baaz on the “arba’eeniyyah” (fortieth day ceremonies). This is originally a Pharaonic custom which was observed by the Pharaohs before Islam, then it spread from them and became widespread among other peoples. It is a reprehensible innovation (bid’ah) for which there is no basis in Islam. It is rejected by the hadeeth of the Prophet (peace and blessings of Allaah be upon him): “Whoever innovates anything in this matter of ours that is not part of it will have it rejected.” Saheeh – agreed upon.
The Messenger (peace and blessings of Allaah be upon him) warned us against innovations when he said: “Beware of newly-invented matters, for every newly-invented matter is an innovation and every innovation is a going astray.” Narrated by Abu Dawood, 4607; classed as saheeh by al-Albaani in Saheeh Abi Dawood. Al-Nasaa’i (1578) added: “And every going astray will be in Hellfire.”
And Allaah knows best.