Is the prayer of a father who leads us in prayer valid if he is wearing shorts above the knee, claiming that a man's 'awrah is only the severe 'awrah, and is our prayer behind him valid?

The 'awrah (intimate parts) of a man are between the navel and the knee, according to the majority of scholars. If a man prays and his trousers cover above his knee, such that his knee is exposed but what is above it is covered, his prayer is valid because the knee is not considered 'awrah by the majority.

However, if he intentionally exposes a part of his thigh, his prayer is invalid according to the majority of scholars, except for the Malikis who consider his prayer valid. Likewise, some scholars believe that the thigh is not 'awrah at all.

As for the prayer of the congregants behind someone whose 'awrah (e.g., thigh) is exposed, their prayer is valid according to some scholars who believe that the prayer of the congregant is not invalidated by the invalidation of the Imam's prayer. This is also the well-known opinion among the Malikis.

Furthermore, some scholars do not obligate repeating the prayer for one who omitted a condition out of ignorance or forgetfulness. It is recommended to advise the worshipper to wear his best clothes out of reverence for the rituals of Allah.