Chapter 72:14
The Sanctity of the Sabbath
14. It is a Mitzvah (1) to wash one's hair and to trim one's nails (on
Friday). Similarly, one should cut one's hair if it has grown long.
One should not cut one's fingernails and toenails on the same day (2).
Similarly, one should not cut one's nails or hair on Rosh Chodesh (1st day
of a new month), even when it falls on Friday (3). Certain people are
careful not to cut their nails in order. Instead, they skip a finger. They
begin with the index finger of the right hand (4). Thus, the order is
2,4,1,3,5. On the left hand, they begin with the fourth finger, following
the order 4,2,5,3,1. There are authorities who are careful not to cut their
nails on Thursday, for then they already begin to grow back on the Sabbath,
the third day afterwards (thus reducing the level of honoring the Sabbath
which was achieved by cutting them) (5).
It is preferable to burn one's fingernails (6).
(1) Part of the Mitzvah to honor the Shabbos.
(2) For those who follow this custom, it is best to cut toenails on
Thursday, and fingernails on Friday (Mishna Berura 260:6).
(3) This was recommended by Rabbi Yehuda HaChassid (1150-1217, Germany),
who is the source of many widely accepted customs based on the Kabbalistic
writings.
(4) Others say to begin with the left hand (Rema 260).
(5) Of course, if its clear that one will not have time to cut them on
Friday, one should certainly cut them on Thursday (Aruch HaShulchan 260:6).
(6) It is permissible to dispose of them in any way you choose (flushing
them down the toilet, etc), but by no means should they be left around
carelessly. The Talmud (Moed Katan 18a) states that fingernails should not
be left lying on the ground, because "perhaps a pregnant woman will step on
them, and have a miscarriage." According to the Zohar, fingernails are
associated with evil and impurity, and were often used in the performance
of black magic.
