After he cleans himself he feels something coming out of the back passage.

If a person relieves himself, cleans himself then does
wudoo’, he is in a state of purity until he is certain that there is
something that has invalidated his wudoo’. His wudoo’ does not become
invalidated because of mere doubts, even if the doubt is so strong that he
thinks it most likely. 

Based on this, merely feeling that something has come out of
the back passage is not counted as invalidating wudoo’. You should also
beware of waswasah (whispers from the shaytaan). So long as you have done
instinja’ and cleaned the place properly, you do not have to check before
praying. 

The prayers that you have offered do not have to be repeated,
because you were in a state of purity and you were not certain that there
was anything that would invalidate it. 

This principle is indicated by the report narrated by
al-Bukhaari (137) and Muslim (361) from ‘Abd-Allaah ibn Zayd (may Allaah be
pleased with him) who said that a man complained to the Messenger of Allaah
(peace and blessings of Allaah be upon him) that he imagined that he
felt something when he was praying, and he said: “He should not stop, unless
he hears a sound or notices a smell.” 

Al-Nawawi (may Allaah have mercy on him) said: This hadeeth
is one of the basic principles of Islam, and an important principle of fiqh,
which is that things are assumed to remain as they are unless there is
certainty that that has changed, and passing doubt does not affect that.  

Another issue related to this hadeeth is that if a person is
certain that he purified himself and is uncertain that it has been
invalidated, then the ruling is that he is still in a state of purity, and
it makes no difference whether this doubt occurs during prayer or outside of
prayer. This is our view and the view of the majority of scholars of the
earlier and later generations. … Our companions said: With regard to doubt
it makes no difference whether the two possibilities with regard to
invalidation of purity are equal or not, or if one of them is more likely,
or he thinks it most likely. He does not have to do wudoo’ in any case. End
quote from Sharh Muslim. 

Shaykh Ibn ‘Uthaymeen (may Allaah have mercy on him) was
asked: When I urinate and do wudoo’ then pray, I feel that something is
coming out of my penis, and when I check it I find that some urine has come
out. What is the solution? 

He replied: Undoubtedly in His wisdom Allaah has made strong
nerves that control urine and faeces so that nothing comes out. But these
nerves may be affected by sickness so that they become weak, then urine
comes out either continuously or occasionally. A person may himself be the
cause of that, because there are some people who, when they finish
urinating, squeeze the urethra to the end of the penis, so as to extract the
urine, and there are some who keep squeezing until the last drop of urine
comes out. This is a mistake, even though some fuqaha’ say that it is Sunnah
to extract the last drop. This is a weak view, and in fact is bid’ah
(innovation), as was stated by Shaykh al-Islam Ibn Taymiyah (may Allaah have
mercy on him) and as is obvious from the Sunnah, because there no report
that the Messenger (peace and blessings of Allaah be upon him) squeezed
the urethra to the end of the penis, or that he squeezed it to extract the
urine. But some people do that, either because they are following the
opinion of the fuqaha’ who said that, or because they imagine that if they
do not do that, there will be some urine left in the penis. But this is a
mistake. If a person urinates and washes the tip of the penis only, that is
sufficient and there is no need to squeeze it or shake it. Rather he should
wash the tip of the penis where the urine has got onto it, and that is the
end of the matter, even if the person has gotten used to doing this because
of this sickness of which he himself is the cause. My advice to him is: if
this happens to you, do not pay any attention to it, do not squeeze the
penis, rather leave it as it is. When the last drop of urine has come out,
he should wash the tip of the penis, and he may feel something in his penis
but he does not have to look, because some people, when they feel something
in the penis, they pull down their trousers and start squeezing the penis
from the end. But if he squeezes it something will inevitably come out.
Rather he should leave it and not pay any attention to it. Some of the
scholars (may Allaah have mercy on them) said: In this case if he is
affected by this waswaas, he should sprinkle some water on his trousers so
that if he thinks or doubts he can assume it is this water. But we say:
there is no need for that, and this is too much. Do not do that, and do not
pay any attention to it, and it will go away in sha Allaah. If you feel some
coolness at the tip of the penis or you feel something in the penis, do not
go and look. Forget about it. End quote from al-Liqa’ al-Shahri. 

And Allaah knows best.