Is it obligatory to obey one's mother regarding not performing the Fajr prayer in the mosque, not growing a beard, and not shortening one's garment, under the pretext of security concerns?

The basic principle is the obligation of congregational prayer, growing a beard, and shortening the lower garment (izar), and it is not permissible to abandon them except for a legitimate excuse. If harm is certain or highly probable to result from growing a beard, attending Fajr prayer, or shortening the izar, then it is permissible to take a concession to the extent of the necessity. In such a case, obedience to the mother is obligatory, because it falls under obedience in what is good, and the Sharia (definition) came to remove hardship. Allah Almighty says: "And He has not placed upon you in religion any difficulty."