Bechoros 24b: Rabbi Yossi ben Hameshulam says: When slaughtering a bechor offering, one should push aside the hair with the knife to uncover the place of shechitah, and one is even allowed to pull out the hair (and it is not forbidden under the prohibition of shearing a bechor). Rabbi Asi said in the name of Resh Lakish: It is only permitted to pull out the hair by hand. But it says with the knife! – Change the words of the Mishnah from “with the knife” to “for the knife”.
רבי יוסי בן המשולם אומר: השוחט את הבכור ־ עושה מקום בקופיץ מיכן ומיכן ותולש את השער. אמר רב אסי אמר ריש לקיש: לא שנו אלא ביד, אבל בכלי אסור. והקתני: עושה מקום בקופיץ מיכן ומיכןִ! תני: לקופיץ.
Someone once asked R’ Chaim Kanievsky, “When I go to put a sefer away on the shelf, and the other seforim are packed closely together, am I allowed to use the sefer in my hand to push the others to the side and make room, or is that a disgrace to the sefer?”
To the questioner’s surprise, R’ Chaim replied, “It is an explicit Mishnah in Bechoros that one may do this. It says that one may use the knife, which is a holy vessel of the Beis Hamikdash, to push aside the hair of a korban. Although the Gemara modifies the text, that is only because pulling out hair using the knife would be forbidden. But using the knife to push aside the hair is permitted. So we see that this is called using a holy object for a holy purpose, since it is a preparation for the avodah. Here too, pushing aside the other seforim is a preparation for putting the sefer back and is permitted.”
He added, “One could ask a similar question about using one’s tefillin to push his shirt sleeve up to make room for the tefillin. And the answer is that it is permitted, as we said.”
Source: Divrei Siach, Vayechi 5781