The Shaytaan whispers to him that he is showing off so that he will give up doing acts of worship

Just as the Shaytaan comes to the Muslim to make him admire
his actions and show off to people, sometimes too he uses the opposite trick
and makes a person think that he is showing off, so that he will not do it. 

In order to avoid both problems, we have to make sure that
our intention is sound and make it sincerely and purely for the sake of
Allaah, and not worry after that about anything that the Shaytaan may come
up with. 

Ibn Muflih al-Hanbali said – in a chapter on “We should not
give up prescribed actions for fear of showing off”: One of the things that
may happen to a person is that when he wants to do an act of worship, it
occurs to him that he should not do it for fear of showing off. 

What he should do is not to pay attention to that. He can do
that which Allaah has commanded him to do or encouraged him to do, and seek
the help of Allaah, and trust in Him that he will do it in the manner
prescribed in Islam. 

Shaykh Muhiy al-Deen al-Nawawi (may Allaah have mercy on him)
said: You should not give up remembering Allaah verbally and in your heart
because you think you may be showing off, rather you should remember Him in
both ways, seeking thereby the Face of Allaah. And he quoted al-Fudayl ibn
‘Iyaad (may Allaah have mercy on him) as saying: Giving up a good deed for
the sake of people is also showing off, and doing it for the sake of people
is shirk. He said: If a person opens the door to noticing people and
worrying about what they think then most of the doors to goodness will be
closed to him.  

Abu’l-Faraj ibn al-Jawzi said: With regard to not doing good
deeds for fear of showing off, if the motive for doing that deed is other
than religious, then he should not do it because it is a sin. But if the
motive for that is religious and it is sincerely for the sake of Allaah,
then he should not refrain from doing it, because the motive is religious.
Similarly if he does not do a good deed for fear that it will be said that
he is a show-off, then he should ignore that because it is one of the tricks
of the Shaytaan. 

Ibraaheem al-Nakha’i said: If the Shaytaan comes to you when
you are praying and says, “you are showing off,” then you should make it
even longer. With regard to the reports narrated from one of the salaf, that
he stopped worshipping for fear of showing off, this is to be understood as
meaning that they felt that they were showing off, so they stopped it. And
that is indeed the case. For example, al-A’mash said: I was with Ibraaheem
al-Nakha’i when he was reading Qur’aan, and a man asked for permission to
enter, so he covered the Mus-haf. He said: So that he will not think that I
read it all the time. So if you should not stop doing an act of worship for
fear of showing off, it is more appropriate that you should not stop it for
fear of self admiration that may occur later on. 

Al-Adaab al-Shara’iyyah,
1/266-267 

Shaykh Ibn ‘Uthaymeen (may Allaah have mercy on him) was
asked: 

When a person thinks of
doing a good deed, the Shaytaan comes and whispers to him: “You want to do
that to show off and have a good reputation,” so he backs off from doing
that good deed. How can we avoid this? 

He replied: 

That can be avoided by seeking refuge with Allaah from the
accursed Shaytaan, and going ahead with the good deed. You should not pay
attention to this waswaas (whisper from the Shaytaan) that puts you off
doing good. If you turn away from this and seek refuge with Allaah from the
accursed Shaytaan, the problem will disappear, by Allaah’s leave. 

Majmoo’ Fataawa al-Shaykh Ibn ‘Uthaymeen,
question no. 277 

And Allaah knows best.