It is not permissible for a Muslim to work in a slaughterhouse in which the sheep are killed by means of electric shock and not slaughtered in the manner prescribed in sharee‘ah, for two reasons:
1.Because this work involves helping in something haraam, which is eating dead meat (that which has not been slaughtered in the prescribed manner). It is established in sharee‘ah that the minor issues of sharee‘ah are also addressed to the kuffaar, so it is haraam for them to eat dead meat just as it is haraam for the Muslims, and it is not permissible to help them in that by slaughtering, carrying or offering the meat.
2.This is destruction of the animal and a waste of its monetary value.
Ash-Shaafa‘i (may Allah have mercy on him) said: If we besiege the mushrikeen and acquire their horses or livestock of any kind, or any creatures belonging to them that it is permissible for Muslims to eat, it is not permissible to stab any of them or kill them in any way except slaughtering them (in the prescribed manner), as Abu Bakr said: “Do not kill any sheep or camel unless it is to eat, and do not drown or burn any palm tree.” I do not think that Abu Bakr went against the Qur’an and Sunnah with regard to animate beings, and neither did any of his peers among the Companions of the Messenger of Allah (blessings and peace of Allah be upon him), as far as I have learned. If the matter involved nothing more than following the example of Abu Bakr, that would be sufficient evidence, although the Sunnah supports what Abu Bakr said with regard to the livestock among their property.
If someone were to ask what the Sunnah is, our response would be that Sufyaan ibn ‘Uyaynah told us, from ‘Amr ibn Dinar, from Suhayb, the freed slave of Banu ‘Aamir, from ‘Abdullah ibn ‘Amr ibn al-‘Aas, that the Messenger of Allah (blessings and peace of Allah be upon him) said: “Whoever kills a small bird or anything bigger unlawfully, Allah, may He be glorified and exalted, will question him about his killing it.” It was said: O Messenger of Allah, what is the legitimate reason (for doing so)? He said: “He should slaughter it (in the prescribed manner) to eat it, and not cut off its head.”
The Messenger of Allah (blessings and peace of Allah be upon him) forbade masboorah (killing a captive animal for “sport”). I find that Allah, may He be glorified and exalted, has permitted killing animals that may be eaten in one of two ways. One way is by slaughtering it in the prescribed manner to be eaten, if one is able to catch it; the other way is killing it with arrows, if one is not able to catch it. But I did not find that He permitted killing it for no purpose. And in my opinion, killing it for any other purpose is forbidden.
End quote from al-Umm, 4/258
The prohibition on masboorah means means capturing it and killing it (for “sport”). Al-Bukhaari (5513) and Muslim (1956) narrated that Hishaam ibn Zayd said: I entered, along with Anas ibn Maalik, the house of al-Hakam ibn Ayyoob, and there were some boys or young men who had made a hen a target and were shooting arrows at her. Anas said: The Messenger of Allaah (blessings and peace of Allah be upon him) forbade taking animals as targets.
Muslim (1959) narrated that Jaabir ibn ‘Abdillah said: The Messenger of Allaah (blessings and peace of Allah be upon him) forbade capturing any animal for the purpose of killing it (for sport).
An-Nawawi (may Allah have mercy on him) said: The Messenger of Allah blessings and peace of Allah be upon him) forbade capturing any animal for the purpose of killing it (for sport); according to another report, he said: “Do not take any animate being as a target.” The scholars said: This refers to detaining a live animal in order to kill it with arrows and the like. This is what is meant by the words, “Do not take any animate being as a target”. In other words: do not take any live animal as a target to shoot at like a target made of leather and the like. This prohibition means that it is haraam. Hence the Prophet (blessings and peace of Allah be upon him) said, according to the report narrated by Ibn ‘Umar that follows this report: “May Allah curse the one who does that.” And because this is tormenting the animal and destroying it, and is a waste of its monetary its value, and missing the opportunity to slaughter it in the prescribed manner, if applicable, and is squandering its benefits if it is not an animal that may be slaughtered for meat. End quote.
Killing animals by means of electric shocks, without slaughtering them in the prescribed manner, is a waste of their value and failing to slaughter them in the prescribed manner. So it is not permissible to do that or to help others in doing it.
And Allah knows best.