The mishnah on Shabbat 42b states:
One may not place a keli under a lamp, on Shabbat, in order to catch the oil that may drip.
Rav Hisda says the principle also applies to a placing a keli under a hen to catch a newly hatched egg:
Rav Yosef explains Rav Hisda on 43a:
By causing a new egg, which is muktsah, to rest on the keli, you are mevattel keli me-heikhano, “nullifying the readiness of the keli.”
Abaye raises a number of cases against Rav Yosef that also involve bittul keli me-heikhano at first glance, including supporting a broken beam in the ceiling with a bench, placing a keli under a leaking roof, and using an overturned basket as a step for baby chicks to enter and exit their coop.
What is this prohibition of bittul keli me-heikhano?
אין נותנין כלי תחת הנר לקבל בו את השמן, ואם נתנוה מבעוד יום - מותר. ואין ניאותין ממנו, לפי שאינו מן המוכן.
One may not place a keli under a lamp, on Shabbat, in order to catch the oil that may drip.
Rav Hisda says the principle also applies to a placing a keli under a hen to catch a newly hatched egg:
אמר רב חסדא: אף על פי שאמרו אין נותנין כלי תחת תרנגולת לקבל ביצתה - אבל כופה עליה כלי שלא תשבר.
Rav Yosef explains Rav Hisda on 43a:
רב יוסף אמר: היינו טעמא דרב חסדא - משום דקא מבטל כלי מהיכנו.
By causing a new egg, which is muktsah, to rest on the keli, you are mevattel keli me-heikhano, “nullifying the readiness of the keli.”
Abaye raises a number of cases against Rav Yosef that also involve bittul keli me-heikhano at first glance, including supporting a broken beam in the ceiling with a bench, placing a keli under a leaking roof, and using an overturned basket as a step for baby chicks to enter and exit their coop.
What is this prohibition of bittul keli me-heikhano?
