1a] Is it permissible for a person who has bought a car or a house to offer a sacrifice in gratitude to Allaah?.

1a]
If one of my children doeswell in school, is it permissible for me to
offer a sacrifice to celebrate his success, and to give thanks to
Allaah?
He replied:
There is nothing wrong with making food (waleemah) if the childrenor
one of them succeeds, and inviting one's loved ones and his child's
friends, to celebrate Allaah's blessing and to encourage the child.
End quote.
Liqaa'aat al-Baab il-Maftooh (no. 161, question no. 1).
Secondly:
It is essential to beware ofsome beliefs which many people hold, and
say that in order to protect the new house or car it is essential to
offer a sacrifice and sprinkle it with the blood of the slaughtered
animal, or that evil spirits will not keep away from you unless you do
that, otherwise the blessing will soon dissipate. hese are jaahili
beliefs which do not come from someone who believes in Allaah as his
Lord Who possesses all powers to bring benefit or cause harm, in Whose
hand is the creation and the commandment, and knows that it is not
permissible to do acts of worship unless they are done for the sake of
Allaah.
The scholars of the Standing Committee wereasked about the belief held
by many people, thatoffering a sacrifice on the threshold of the new
house before entering it isone of the most important means of warding
off the evil eye, and making the house blessed, and avoiding
calamities and undesirable events.
They replied:
If this custom – i.e., offering a sacrifice on the threshold of the
new house – is done in order to placate the jinn and ward off
calamities and undesirable events, then it is a haraam custom, andis
in fact shirk. This is what seems to be the case with offering the
sacrifice before entering the house, and doing it onthe threshold in
particular.
But if the intention is to honour one's new neighbours and get to know
them, and to give thanks to Allaah for the blessing of a new home, and
to honour one's relatives and friends on this occasion, and to
showthem the house, then this is good and the one who does it is to be
praised forhis action. But that is only usually done after the people
have moved into the house, and not before,and the animal or
animalsshould not be slaughteredon the threshold of the house or in
the entryway to the house. End quote.
Fataawa al-Lajnah al-Daa'imah (1/214)
See also the answer to question no. 26952 , which quotes two fatwas
from Shaykh 'Abd al-'Azeez ibn Baaz and Shaykh al-'Uthaymeen
concerning the same topic.
And Allaah knows best.