Dought & clear, - His parents think that he does not offer the naafil prayers, but he prays them in secret for fear of showing off. Should he tell them about that?

My parents usually scold me whenever i do not pray the optional
prayers after the fardh prayer. I actually pray these prayers at home
after returning from masjid and my parents think i dont pray because i
return faster from the masjid after i get scoldings. When i am scolded
i obediently listen but do not reply because i feel when i will tell
them that i do a better thing by praying the optional prayer at home,
i will show off which is haraam. I am also aware that they will be
pleased by hearing that i do a better thing. Kindly suggest on whether
i should continue as i am doing (leave them dissapointed) or should i
inform them that i do pray at home (may be a show off).
Praise be to Allah.
Firstly:
Concealing acts of worship and not doing them openly is better than
doing them openly and announcing them. Allah, may He be exalted, says
(interpretation of the meaning):
"If you disclose your Sadaqat (alms-giving), it is well, but if you
conceal it, and give it to the poor, that is better for you. (Allah)
will forgive you some of your sins. And Allah is Well-Acquainted with
what you do"
[al-Baqarah 2:271].
Ibn Katheer (may Allah have mercy on him) said: The words "but if you
conceal it, and give it to the poor, that is better for you" indicate
that giving charity in secret is better than giving it openly, because
that is further removed from showing off, unless giving it openly will
serve a greater purpose by setting an example for people, in which
case it is better in that respect.
End quote fromTafseer al-Qur'an al-'Azeem, 1/701
Secondly:
The Sunnah indicates that it is better to offer the naafil prayers at
home. Al-Bukhaari (6113) and Muslim (781) narrated that the Prophet
(blessings and peace of Allah be upon him) said: "You should pray in
your houses, for the best of a man's prayer is in his house, apart
from the obligatory prayers."
The scholars (may Allah have mercy on them) stated that one of the
benefits of that is that praying at home is closer to sincerity and
further removed from showing off.
Ibn Qudaamah (may Allah have mercy on him) said: Offering voluntary
prayers at home is better, because the Messenger of Allah (blessings
and peace of Allah be upon him) said: "You should pray in your houses,
for the best of a man's prayer is in his house, apart from the
obligatory prayers."Narrated by Muslim. It was narrated from Zayd ibn
Thaabit (may Allah be pleased with him) that the Prophet (blessings
and peace of Allah be upon him) said: "A man's prayer in his house is
better than his prayer in this mosque of mine, apart from the
obligatory prayers." Narrated by Abu Dawood. And that is because
praying at home is closer to sincerity and further removed from
showing off.
End quote fromal-Mughni, 1/443
For more information, please see the answer to question no. 22209
Thirdly:
If not telling your parents will result in what you mentioned, then in
this case it is better to tell them, so as to ward off suspicion and
negative thinking of you. Moreover, perhaps by telling them – as you
said – it will make them feel happy, and making parents feel happy, by
obeying them and doing good, is part of honouring them, which is
something that is prescribed and that one should be eager to do.
With regard to the fear of showing off, you have to strive to make
yourself sincere, and ask Allah, may He be glorified and exalted, to
help you to do that.
May Allah help us and you to be sincere in worshipping Him, may He be
exalted, and may He protect us all from the evil of our own selves,
for He is able to do that.
And Allah knows best.