It is clear that one may not pray, recite a Beracha, or learn Torah in a restroom or in the presence of bodily waste. But is one allowed to perform a Misva, or to make plans for performing a Misva, in such a place?
One example might be Sedaka (charity). Is a person permitted to write checks to charity while in the restroom, or to go over his finances to calculate how much to donate to different organizations?
Another example is a person who is in prison, and the toilet is in his cell. If the Jewish chaplain was able to bring him a Lulab and Etrog during Sukkot, may he perform the Misva of Arba Minim (the four species) – of course without reciting a Beracha – there in the cell, which also serves as his restroom?
The Ben Ish Hai (Rav Yosef Haim of Baghdad, 1833-1909) writes that one may not make plans for performing a Misva while in the inner chamber of the bathhouse (which has the same status as a restroom). This includes planning his Shabbat preparations, his purchase of the four species, or distribution of charity. Hacham Ovadia Yosef, however, challenged this ruling, in light of a passage in the Talmud Yerushalmi (Demai 1:4) which permits separating Ma'aserot (tithes) in a bathhouse in situations where no Beracha is required (namely, when one tithes Demai – produce which must be tithed as a precautionary measure). This clearly demonstrates that although Berachot may not be recited in a bathhouse, Misvot may be performed.
Clearly, one should preferably strive to perform all Misvot in a clean area, out of respect for the Misva. When, however, a person has no choice – such as in the case of a prison inmate – he may perform Misvot even in the presence of filth. Additionally, while a Misva should preferably not be performed in an unclean place, one may make preparations for performing Misvot in such a place. Moreover, Hacham Ovadia ruled that when it comes to a Misva like charity, which one can fulfill without thinking of spiritual matters – because the essence of the Misva is the practical assistance given – one may fulfill such Misvot even in the presence of filth. Therefore, one may write checks to charity organizations while in the restroom.
Summary: Although it is preferable to perform Misvot in a clean area, one may, when necessary, perform a Misva in an unclean place. Thus, for example, a prison inmate who is brought the four species on Sukkot may perform the Misva in his cell even though his toilet is there. One may make plans in the restroom for a Misva – such as planning Shabbat preparations, the building of his Sukka, and so on. One may also write checks for Sedaka while in the restroom.