What is the ruling on financial compensation for guarding and invigilating the Arabic language exam, the subject of which revolves around the ney and musical instruments?

If the measured subject is the Arabic language, then the exam assesses knowledge of the language regardless of the topic of the literary texts. There is no blame upon the questioner concerning the financial compensation associated with this work, because he has not directly committed an abomination nor has he directly or intentionally assisted in one.