Is it permissible to send a sick leave certificate to the company—even though the sender is not ill—and forgo a full day's pay, in order to attend Friday prayer?

The Friday prayer is obligatory for every healthy, mature, resident man. It is strictly forbidden to abandon it. Whoever abandons three Friday prayers out of negligence, Allah will seal his heart.

If it is possible to perform the Friday prayer at work, it is not permissible to lie by claiming illness. If the employer prevents attendance, it is forbidden for him to do so, as the time for Friday prayer is legally exempt from employment contracts. In this situation, it is permissible to be absent from work by stratagem, provided that no daily wage is taken unless one is truly ill and there is an agreement to pay wages during illness. One can request a medical certificate from a doctor for any minor ailment like a headache.