When hair falls out from someone’s beard, is it necessary to put it in a sefer? It always made me uncomfortable opening a sefer and seeing hairs from a beard.
There are various sources that indicate that this was a common practice amongst tzadikim, due to the holiness of their beard.
However in more recent times, many Poskim have decried this custom, especially when placing into a sefer that does not belong to oneself, due to its being repulsive, disrespect to the sefer, causing bitul Torah (prevents others from using it), etc.
This is especially true if one would normally throw the hair away, but places it in a sefer only while learning.
ראה הנלקט בקובץ בית ועד לחכמים (קרית יואל) ח”ו ע’ תיב ואילך. והאריך בזה בס׳ שערים מצויינים בהלכה לאחי שליט״א זבחים יח, ב – ע׳ קסב.