Eating beef that has not been slaughtered properly until after it has been killed

Beef that has been killed before being slaughtered (i.e., before its
neck is cut in the halaal method) is considered to be maytah
(“dead meat”) and it is not permissible to eat it, because Allaah says
(interpretation of the meaning): 

“He has forbidden you only Al Maitah
(meat of a dead animal), blood, the flesh of swine, and any animal which
is slaughtered as a sacrifice for others than Allaah (or has been slaughtered
for idols or on which Allaah’s Name has not been mentioned while slaughtering).
But if one is forced by necessity, without wilful disobedience, and
not transgressing, then, Allaah is Oft Forgiving, Most Merciful

[al-Nahl 16:115] 

With regard to what you mention about some Muslims eat meating that
has been killed before being slaughtered, it may be that they are sure
that the meat that they are eating has been slaughtered according to
sharee’ah, or it may be that they are ignorant of the rulings on this
kind of meat, or they may have asked (scholars) who told them that this
meat is halaal. 

Whatever the case, you have to avoid eating these meats, and if anyone
asks you to eat it, you should refuse to do so, and explain why you
are refusing – so that they will follow that or at least excuse you
for not eating it. 

With regard to what you mention about some people saying that it is
permissible to eat this meat because they are the People of the Book,
the answer is that it is permissible to eat meat that has been slaughtered
by the People of the Book, but this meat that you describe is not meat
that has been slaughtered by them; rather it is dead meat, and it is
not permissible to eat dead meat even if it was killed by a Muslim. 

Shaykh ‘Abd al-‘Azeez ibn Baaz (may Allaah have mercy on him) said: 

“Allaah says (interpretation of the meaning): 

‘Made
lawful to you this day are At Tayyibaat [all kinds of Halaal (lawful)
foods, which Allaah has made lawful (meat of slaughtered eatable animals,
milk products, fats, vegetables and fruits)]. The food (slaughtered
cattle, eatable animals) of the people of the Scripture (Jews and Christians)
is lawful to you and yours is lawful to them’

[al-Maa’idah 5:5] 

This aayah makes it clear to us that the food of the People of the
Book – i.e., the Jews and Christians – is permissible for us, but if
we know that they have slaughtered a permissible animal in a manner
other than that prescribed in sharee’ah, such as killing it by strangulation,
electric shock, hitting it on the head, etc., then it is meat “which
has been killed by strangling, or by a violent blow” (cf. al-Maa’idah
5:3), so it is haraam, just as meat which has been killed by strangling,
or by a violent blow by a Muslim is also forbidden to us. But if we
do not know what is the case, then the meat slaughtered by them is halaal
for us, in accordance with the aayah.” 

(Majallat al-Jaami’ah al-Islamiyyah, no. 3, p. 156 

In conclusion, we hope that
you will spread the fatwa of Shaykh ‘Abd al-‘Azeez ibn Baaz to the Muslims
whom you know, as much as you can. And Allaah knows best.