Firstly:
Is wudu invalidated if worms come out of the back passage?
The majority of Hanafi, Shafa`i and Hanbali scholars, and some of the Malikis, are of the view that if worms come out of the back passage, that invalidates wudu.
Ibn Qudamah (may Allah have mercy on him) said:
Whatever comes out of the front and back passages is of two types, one of which is that which ordinarily comes out, such as urine, faeces, maniy (semen), madhiy (prostatic fluid), wadiy and wind. This invalidates wudu according to scholarly consensus…
The second type is that which is rare, such as blood, worms, stones and hair. This also invalidates wudu. That is the view of ath-Thawri, ash-Shafa`i, Is-haq and as-hab ar-ra’y. ‘Ata’, al-Hasan, Abu Majlaz, al-Hakam, Hammadi, al-Awza`i, and Ibn al-Mubarak narrated that wudu is required if worms come out of the back passage, whereas Malik did not think that wudu was required for this type, because it is rare…
End quote from Al-Mughni, 1/230.
It says in Al-Mawsu`ah al-Fiqhiyyah al-Kuwaitiyyah, 17/112:
That which comes out of the front and back passages rarely, such as worms, stones, hair, pieces of flesh and the like, is regarded as minor impurity which invalidates wudu according to the majority of jurists (the Hanafis, Shafa`is and Hanbalis). This is also the view of Ibn `Abd al-Hakam among the Malikis.
This was also the view of ath-Thawri, Is-haq, ‘Ata’ and al-Hasan, because it comes out of the front or back passage, so it is akin to madhiy. End quote.
Shaykh Ibn `Uthaymin said in his Ta`liqat `ala al-Kafi li Ibn Qudamah (1/128):
The correct view is that there is no difference between that which ordinarily occurs and that which rarely occurs. So if stones, worms, hair and the like come out of the back passage, it invalidates wudu. The evidence for that is the words of the Prophet (blessings and peace of Allah be upon him): “… unless you hear a sound or notice a smell.” If wind, which has no substance, invalidates wudu, then it is more appropriate to say that that which has substance also invalidates wudu. End quote.
Shaykh Dubyan ad-Dubyan said: It seems that what matters is where it comes from, not whether it is impure or not, because wind is pure, but if it comes out of the back passage, it invalidates wudu, but if it comes out of the mouth (that is, burping), it does not invalidate wudu; what matters is not whether it is something that ordinarily happens or not, because wadiy is something that happens rarely and is not common, and it may be indicative of a health issue, yet despite that it invalidates wudu even according to the view of Malik (may Allah have mercy on him).
End quote from Ahkam at-Taharah, 10/631.
Secondly:
Is it obligatory to clean oneself (istinja’) if worms come out of the back passage?
Although it is proven that if worms come out of the back passage, that invalidates wudu, it does not make it obligatory to clean oneself, because the reason for cleaning oneself (istinja’) is the presence of impurity, and the purpose behind cleaning oneself with water or pebbles is to remove substance of the impurity from the surface of the body.
Hence the majority of scholars are of the view that cleaning oneself is not required if worms come out, except in the case where they contaminate the anus and the surrounding area with impurity. But if they do not contaminate the anus, then there is no requirement to clean oneself if they come out.
It says in Hashiyat ad-Dasuqi (1/113), which is a book of Maliki jurisprudence:
Similar to wind in the sense that there is no requirement to clean oneself are: stones and worms, if they come out free of moisture, or the amount of moisture is small.
But if they come out with a great deal of moisture, then it is obligatory to clean oneself with water or pebbles, even if they do not invalidate wudu, as we shall see below. End quote.
Ar-Rafi`i ash-Shafa`i (may Allah have mercy on him) said:
If something comes out of the passage, it should be examined: if it is not contaminated [with impurity], such as worms or stones on which there is no moisture, then there are two scholarly views as to whether it is required to clean oneself. The more sound of the two views is that it is not required to clean oneself with either water or pebbles, because the purpose of cleaning oneself is to remove the impurity from that place or reduce it. So if the place is not contaminated and did not become impure, then there is no sense in trying to remove or reduce the impurity…
End quote from Fat-h al-`Aziz, 1/477.
Al-Mardawi al-Hanbali (may Allah have mercy on him) said:
With regard to impurity that does not cause contamination, there is no difference of scholarly opinion regarding the fact that it is obligatory to clean oneself of it. As for impurity that does not cause contamination and that which is pure, the correct view in our madhhab, which is also the view of the majority of our companions, is that it is obligatory to clean oneself of it.
And it was said that there is no requirement to clean oneself of something pure that comes out, or something that is impure but it did not contaminate the place…
By analogy, there is no obligation to clean oneself from that which comes out dry and does not contaminate the area. The same applies if what comes out is pure, such as maniy (semen), if we deem it to be pure, because cleaning oneself (istinja’) is only prescribed in order to remove impurity, and there is no impurity in this case. It says in Al-Furu`: This is more likely to be the correct view. It says in Ar-Ri`ayah al-Kubra: This is more correct based on analogy. I say: it is the correct view. How can someone clean himself with water or pebbles from something that is pure? Or how can he clean himself with pebbles from something that came out and did not cause any contamination? Does that make any sense?
End quote from Al-Insaf, 1/232-234.
Shaykh Ibn `Uthaymin (may Allah have mercy on him) said:
… There is no requirement to clean oneself of what is pure. Also exempted is that which does not cause contamination because it is dry. So if something comes out that does not cause contamination because it is dry, there is no requirement to clean oneself of it, because the purpose of cleaning oneself (istinja’) is to purify oneself, but in this case there is no need for that. But if something rare, such as a stone, comes out, is it obligatory to clean oneself?
The answer to that is: if it causes contamination, then it is obligatory to clean oneself, because it comes under the general meaning of the author’s words. But if it does not cause contamination, there is no obligation to clean oneself because there is no need for that.
End quote from Ash-Sharh al-Mumti`, 1/140-141.
It says in Al-Mawsu`ah al-Fiqhiyyah, 4/116:
If what comes out is something unusual, such as stones, worms or hair, there is no requirement to clean oneself of it if it comes out dry, whether it is regarded as pure or impure.
But if it has some moisture and contaminates the place, then you must clean yourself of it, but if it does not contaminate the area, there is no need to clean oneself of it according to the Hanafis and Malikis; this is also the earlier view of both the Shafa`is and Hanbalis. End quote.
Based on the above, what you mention about your feeling the worms come out even though you were not able to see them means that there is no requirement to clean yourself, because in this case only two scenarios may apply:
Either your feeling that was not correct; rather it was only an itch or some sensation in that place, and no attention is to be paid to such things.
Please see the answer to question no. 89888.
Or you were not able to see them because they are very small. In that case it cannot be imagined that it would contaminate the place where it came out, and it would not leave behind any contamination that could be seen, so there is no requirement to clean oneself of it because there is no proof that any impurity is present.
But we should point out that what matters is not looking at the worms that come out; rather you should look at the place and see whether there is any contamination from the worms in the first place. This is something that you can find out and determine, even if it is by wiping the area with a tissue and the like, if you are not sure whether there is any contamination.
And Allah knows best.
