Ruling on blood that gets on the butcher at the time of slaughter

Firstly: 

“Blood poured
forth” (6:145) is najis (impure) according to scholarly opinion. This has
been discussed previously in the answer to question no.
114018. “Blood poured forth”
is that which comes out of the animal at the time of slaughter. 

As for the blood
that is mixed with the meat or that remains in the veins, it is not called
“blood poured forth”. 

Secondly: 

What is required
is to purify the clothes on which there is blood, or to change them, before
starting to pray, because one of the conditions of prayer being valid is the
removal of impurities from one’s garments or body or from the place where
one prays, because the Prophet (blessings and peace of Allah be upon him)
said: “If one of you comes to the mosque, let him look, and if he sees any
dirt or impurity on his shoes, let him wipe it off and pray in them.”

Narrated by Abu
Dawood (650); classed as saheeh by al-Albaani in Saheeh Abi Dawood. 

But most of the
scholars (may Allah have mercy on them) restricted that to cases where there
is a lot of the impurity; if there is only a little you do not have to wash
it, because it is too difficult to avoid it. 

It says in
Mukhtasar Khaleel wa Sharhuhu: 

A spot of actual
blood less than the size of a dirham is overlooked blood traces (of
impurities) may be overlooked even if they are larger than the size of a
dirham. This applies whether it is blood from menses, nifaas (postpartum
bleeding), an animal that died naturally or a pig, from the body or from
outside of it, on his own garment or the garment of another or on his body,
in prayer or otherwise.

Sharh Mukhtasar
al-Khaleel
by al-Kharashi, 1/107 

Al-Hajaawi (may
Allah have mercy on him) said: In the case of things other than liquids or
food that are to be drunk or eaten, a small amount of najis blood from
animals that are taahir (pure, i.e., permissible to eat) may be pardoned. 

Shaykh Ibn
‘Uthaymeen (may Allah have mercy on him) said: Pardoned means that it is
overlooked and tolerated. Liquids refers to things such as water, milk and
broth. Food refers to things that are eaten such as bread and the like. 

What is referred
to with regard to things other than these two, such as garments, bodies,
furniture, the ground and so on, is that a small amount of najis blood may
be overlooked.

End quote from
ash-Sharh al-Mumti‘, 1/439 

More than one of
the fuqaha’ have clearly stated that butchers and others who carry out
similar professions may be excused for small amounts of impurities that get
onto their bodies and clothes because of their work, especially if they try
hard to avoid that and remove whatever gets onto them of it, or it is too
difficult for them to change their clothes in order to pray. 

It says in
Sharh Mukhtasar Khaleel by al-Dardeer (may Allah have mercy on him): 

If she (a mother
with a small infant) tries hard to avoid urine or stools by removing it as
soon as (the baby) urinates, or by wrapping a cloth (such as a diaper)
around him that will prevent it reaching her, then if anything gets on her
after taking precautions, it may be overlooked. But it cannot be overlooked
if she did not take precautions. The same applies to the lavatory cleaner
and butcher. Ad-Dasooqi (may Allah have mercy on him) said in his
Haashiyah: 

The words “and
similarly the lavatory cleaner” refer to the one who empties the tank of
waste. And in the case of (the lavatory cleaner and) the butcher who
slaughters animals, they may be excused for whatever (impurities) get onto
them provided they take precautions; if they did not take precautions then
they cannot be excused. They have to wash off the impurity if they are
certain or think it likely that it got onto them, but they may sprinkle
water on it if they are uncertain. The words “the same ruling applies to
other people in similar situations” mean situations similar to those of the
lavatory cleaner and the butcher. The words “because it is unavoidable for
them” mean that it is not completely under their control and they cannot
avoid the impurities altogether.

End quote from
ash-Sharh al-Kabeer wa Haashiyat ad-Dasooqi ‘alayhi, 1/72 

Al-‘Allaamah Ibn
‘Aabideen
(may Allah have mercy on him) said:  

A similar case to
urine is blood on the clothing of the butcher. The reason why only the
butcher is mentioned is that in the case of anyone other than the butcher it
is not to be overlooked, because the reason for the concession in his case
is a necessity and that is not a necessity for others.

End quote from
Radd al-Muhtaar, 1/322; see also 1/324. See also al-Mawsoo‘ah
al-Fiqhiyyah, 40/113 

With regard to
what is regarded as a small amount or large amount, reference should be made
to custom. 

Shaykh Ibn
‘Uthaymeen (may Allah have mercy on him) said: What matters is what the
people think; whatever they regard as a lot is a lot and whatever they
regard as a little is a little. 

End quote from
ash-Sharh al-Mumti‘, 1/272 

And Allah knows best.