What is the ruling on working as a teaching assistant at a music institute and working as a violin player in studios, while being careful to seek lawful earnings and avoid doubtful matters?

Seeking what is lawful (halal) is a religiously mandated act, and its practitioner is praised for it. "And whoever fears Allah – He will make for him a way out and will provide for him from where he does not expect." (Quran 65:2-3) As for insisting on unlawful or dubious work, it exposes its doer to Allah's wrath.

Singing and music are forbidden, and working as a musician, playing musical instruments, is unlawful earnings according to Islamic law because it is not a religiously respected profession. Many jurists have rejected the testimony of singers and musicians, considering it an act of moral transgression (fisq). Jurists have regarded instruments of amusement and entertainment as tools for sin.

The questioner is advised to seek another job, turn to Allah in supplication, engage in trade with what he possesses, even if it is little, or look for another job, even if it offers a lower salary.