Cutting Fingernails and Toenails on the Same Day
Question
Is it permissible to cut fingernails and toenails on the same day when necessary?
Answer
It is permissible on Friday and for the purpose of a mitzvah immersion.
Source
The prohibition against cutting fingernails and toenails on the same day comes from the Knesset HaGedolah, who wrote that there is a danger in this.
The permission on the eve of Shabbat is found in the Mishnah Berurah, Siman 260, Se'if Katan 6, which states: "Some have written not to cut fingernails and toenails on the same day, and one should only cut them on Friday or the eve of a festival, and it is proper to cut toenails on Thursday and fingernails on Friday [M"A]"
And for a mitzvah immersion, it is clear in Siman 198. The Ketzot HaShulchan wrote that one who observes a mitzvah will know no evil.
