It is reported that Abū Hurayrah – Allāh be pleased with him – said:

Three things are from Imān: when a man has nocturnal emission during a cold night, so he gets up – only Allāh sees him, and has a full wash; when a person fasts on a hot day; and when a man prays in a barren land, where none but Alāh sees him.

Al-Bayhaqī, Shu’ab Al-Īmān article 51