What is the ruling on a young man praying Fajr at home – if the mosque is nearby – if his father prevents him from going to the mosque, fearing that authorities might harass those who pray Fajr?

Congregational prayer in the mosque is obligatory according to the soundest opinions of scholars. Evidence for this includes the hadith of the blind man, whom the Prophet (peace and blessings be upon him) did not permit to miss it, and the hadith where the Prophet (peace and blessings be upon him) considered burning the houses of those who failed to attend it. It is not permissible to miss congregational prayer except for a legitimate Shar'i excuse, such as illness, rain, or a fear that is certain or highly probable. However, if the matter is merely a baseless apprehension, then it is not permissible to obey one's father in missing the congregational prayer, because obedience is not due in disobedience to the Creator.