The difference between the ruling on swallowing sputum and its effect on the fast, and swallowing a pebble

The most correct scholarly view is that
swallowing sputum does not invalidate the fast, as was previously explained
in fatwa no. 172499. This does not contradict the
fact that fasting is invalidated by swallowing anything, even if it is not
food, such as pebles and the like. 

It says in al-Haawi al-Kabeer
(3/456): ash-Shaafa‘i (may Allah be pleased with him) said: If he swallows a
pebble or something that is not food, or uses a suppository, or treats a
wound and (the medicine) reaches his stomach, or he uses snuff and it
reaches the inside of his head, then he has broken the fast if he remembered
(that he was fasting), but there is no blame on him if he forgot. 

Al-Maawardi said: And that is the case if he
swallows food or drink or something that is neither food nor drink, such as
a dirham (silver coin) or a pebble, or a walnut or an almond, then he has
broken the fast by doing any of these things, and he must make up that day
if he did it deliberately, remembering that he was fasting; but if he did it
because he had forgotten, then his fast remains valid. End quote 

This issue has been discussed previously in
fatwa no. 78479 

The reason why there is no contradiction is
that sputum comes from inside the body and it is part of his physical being,
so if a person swallows it, it cannot be said of him that he has swallowed
something from outside his body. This is unlike the case with a stone and
the like; the one who takes it and swallows it has taken something from
outside his body, so his fast is invalidated thereby. 

Ibn Habeeb said: Whoever clears his throat
then swallows his sputum after it reaches the edges of his tongue, there is
no blame on him, but it is not appropriate, because sputum is not food or
drink, and it originates inside the head. Al-Baaji said: The point that Ibn
Habeeb was trying to make is that he did not pick it up from the ground;
rather he let it collect in his mouth in a normal manner, like saliva;
otherwise it is makrooh to swallow it because it is possible to spit it out,
unlike saliva.

End quote from at-Taaj wa’l-Ikleel
(2/426) 

Shaykh Muhammad al-Hasan ad-Daddu
ash-Shinqeeti says: What is in the mouth is viewed like anything else inside
the body according to the more correct view, therefore it does not become
najis (impure) unless it comes out of the mouth. With regard to that which a
person did not put in his mouth from the outside, rather it came from inside
the mouth or is part of his physical being, the correct view is that it does
not invalidate the fast. Saliva, sputum and the like are things that come
from inside the body; hence that does not invalidate the fast, because they
are not nourishment from outside. This is the more correct opinion.

End quote from the following link:

http://ar.islamway.net/fatwa/10488 

Sputum that is in the nose as a result of
sniffing with the nose, then he lets it get into his mouth, then he swallows
it, does not invalidate the fast according to the more correct view. It says
in Tabyeen al-Haqaa’iq Sharh Kanz ad-Daqaa’iq (1/324): If he sniffs
back the sputum from his nose until he lets it get into his mouth, and
swallows it deliberately, that does not invalidate the fast. End quote. 

In al-Bahr ar-Raa’iq Sharh Kanz
ad-Daqaa’iq (2/294) it says: If sputum enters the fasting person’s nose
from inside his head, then he sniffs it back and it enters his throat as a
result of a deliberate action on his part, there is no blame on him, because
it is the same as his saliva; unless he puts it in his hand then swallows
it. In that case he has to make up that day. And in az-Zuhayriyyah it
says that the same applies to sputum and spittle that comes out of his mouth
or nose, then he sniffs it back, iIt does not invalidate his fast. End
quote. 

However we have previously pointed out that
sputum is something that is usually regarded with disgust, so he should not
swallow it if he is able to expel it. 

More than one of the scholars have pointed
out that one should take into consideration the view that says that doing so
invalidates the fast, because it is not difficult to pay attention to that. 

Al-‘Allaamah ash-Sharanbilaali al-Hanafi
(may Allah have mercy on him) said: 

Concerning the evidence, Ibraaheem was asked
about one who swallows his sputum. 

He said: If it is less than a mouthful, it
does not invalidate the fast, according to consensus [i.e., among the
Hanafis]. 

But if it fills his mouth, then it does
invalidate his fast, according to Abu Yoosuf; but according to Abu Haneefah
it does not invalidate his fast, but he should expel the sputum so that it
does not invalidate his fast, according to the view of Imam ash-Shaafa‘i, as
was pointed out by al-‘Allaamah Ibn Shahnah, so that his fast will be valid
according to scholarly consensus, because he is able to expel it.

End quote from Maraaqi al-Falaah Sharh
Noor al-Eedaah (246) 

And Allah knows best.