Is it permissible to pray in a shirt that covers the entire body without an undershirt or trousers beneath it, and does the prayer become invalid if a part of the awrah (private parts) becomes exposed from the neck opening during prostration to someone who focuses their gaze?

It is preferable for the worshipper to wear more than one garment for complete covering and adornment, and this is a saying of 'Umar, may Allah be pleased with him. Prayer is permissible with a single garment (qamis) if it covers the 'awrah. However, if the 'awrah becomes visible from the neck opening during bowing and prostration, the prayer becomes invalid and must be repeated. Some scholars hold the view that the prayer of one who omits a condition or a pillar due to ignorance or forgetfulness is valid.