הלכה על קידושין 61:12

A woman who wishes to voluntarily fulfill the positive time-bound mitzvot receives reward for doing so, although it is not the same as a man’s reward. As R. Ḥanina states, “Greater is the [reward for] one who is commanded to do and does than one who is not commanded and does” (Kiddushin 31a). Ritva explains that the reason for this is that one who is commanded to perform a mitzva encounters the resistance of his; therefore his reward is greater, as the Sages say, “lefum tza’ara agra” (according to the torment is the reward) (m. Avot 5:23).