Is it permissible for my husband to combine prayers after returning from work due to his difficult working conditions (such as severe cold and soiled clothes), his employer preventing him from praying, and him suffering harm in his livelihood if he leaves the job, knowing that he prays Fajr before its time based on a fatwa from his mother?

Performing the Dawn (Fajr) prayer before its prescribed time or delaying it until sunrise is not permissible. Rather, it must be performed within its time, and delaying it without a valid excuse is a major sin. As for the Noon (Dhuhr) and Afternoon (Asr) prayers, they must be performed within their times. However, it is permissible for your husband to combine them (perform them together) if there is a need and a fear of harm to his livelihood. Your husband must perform the prayer when its time begins, and it is not permissible for him to abandon it or perform it before its time, except in cases of combining prayers. It is not obligatory to change clothes for prayer unless they are ritually impure (najis). If they are najis and he is unable to change them, then let him pray in them. Let him perform ablution (wudu), and if he is unable, then let him perform dry ablution (tayammum). An employer does not have the right to prevent him from praying. If the husband is unable to pray on time due to work, he must leave this job and search for another that does not prevent him from praying.