Voluntarily (adverb) — طوعاً أو اختيارياً: Of one's own free will. Below are 6 words with a similar meaning; the linked ones have full GL Dictionary entries with their meaning in Arabic.
Readily and without being forced.
freelyby choiceof one's own accordspontaneouslyreadily
On your own initiative, without being told.
GL usage: done willingly by one's own choice, not under pressure.