If he sneezes or hears a donkey braying whilst praying, should he say the dhikr narrated in the Sunnah?

Question

Praise be to Allah.

With regard to sneezing, it is narrated in the Sunnah that a
worshipper should say al-hamdu Lillaah if he sneezes.

With regard to seeking refuge with Allaah from the accursed
Shaytaan when hearing a donkey braying (whilst one is praying), there is no
report in the Sunnah to that effect.

Shaykh Ibn ‘Uthaymeen
said:

If a person sneezes whilst praying, he should say Al-hamdu
Lillah, as was narrated in the saheeh report of the story of Mu’aawiyah ibn
al-Hakam (may Allaah be pleased with him) when he started to pray with the
Prophet (peace and blessings of Allaah be upon him), then a man among
the people sneezed and said, “Al-hamdu Lillaah.” Mu’aawiyah said to
him, “Yarhamuk Allaah (may Allaah have mercy on you).” The people
glared at Mu’aawiyah, denouncing him for speaking. He said: “May my mother
be bereft of me!” then they started to beat their hands on their thighs,
indicating to him to be quiet, so he was quiet. When the prayer was over,
the Prophet (peace and blessings of Allaah be upon him) called him.
Mu’aawiyah said: May my father and mother be sacrificed for him. By Allaah,
he did not scold me or beat me or rebuke me. He said: “This prayer should
not include anything of people’s talk; rather it is tasbeeh (saying ‘Subhaan
Allaah’ – glory be to Allaah), takbeer (saying ‘Allaahu akbar’ – Allaah is
Most Great) and reciting Qur’aan.” Narrated by Muslim, 537; Abu Dawood,
930.

The Prophet (peace and blessings of Allaah be upon him)
did not tell off the one who sneezed and said Al-hamdu Lillaah whilst
praying, which indicates that if a person sneezes during the prayer he
should say al-hamdu Lillaah, because there is a reason for doing so.
But that does not apply to every dhikr for which the reason for saying it
occurs whilst one is praying.

Fataawa Ibn ‘Uthaymeen, 13/342.

And he was asked:

Is it permissible for one who is praying to say al-hamdu
Lillaah if he sneezes, and to seek refuge with Allaah if he hears a
donkey braying? Is there a difference between obligatory prayers and naafil
prayers in that regard?

He replied:

With regard to saying al-hamdu Lillaah if he sneezes
and seeking refuge with Allaah if he hears a donkey braying, that is
permissible according to the view favoured by Shaykh al-Islam Ibn Taymiyah
(may Allaah have mercy on him), but it is makrooh according to the well
known view of the madhhab of Imam Ahmad. The more correct view is that
favoured by Shaykh al-Islam with regard to saying al-hamdu Lillaah if
one sneezes. With regard to seeking refuge with Allaah when hearing a donkey
braying, it is better not to do that. The difference between them is that
saying al-hamdu Lillaah when sneezing is mentioned in the Sunnah, and
because it is prescribed by a specific command, unlike when a donkey brays,
which is does not concern him, and the worshipper should not let himself be
distracted by sounds outside the prayer.

With regard to the above,
it makes no difference whether the prayer is a prescribed (obligatory)
prayer or a naafil (supererogatory) prayer.”

Fataawa Ibn ‘Uthaymeen, 13/342.

And Allaah knows best.