Exodus 12:22

אזוב HYSSOP — a kind of herb which has thin stalks. אגדת אזוב A BUNCH OF HYSSOP — three stalks are called a bunch (cf. Shabbat 109b; Sukkah 13a). אשר בסף means WHICH IS IN THE VESSEL, as in (2 Kings 12:14) “basins (ספות) of silver.” מן הדם אשר בסף WITH THE BLOOD WHICH IS IN THE BASIN — Why does Scripture repeat this (אשר בסף) again? In order that you should not say that one dipping of the hyssop in the basin suffices for the three sprinklings, therefore it is again stated: “[you shall touch the lintel…] “with the blood that is in the basin”, to show that each separate sprinkling must be with the blood which is in the basin — for each touching of the lintel and doorposts there must be a separate dipping (Mekhilta). ואתם לא תצאו וגו׳ AND NONE OF YOU SHALL GO OUT etc. — This tells us that when once permission is given to the destroying angel to wound he makes no distinction between righteous and wicked (Mekhilta) — and nighttime is the domain of the destroying agencies as it is said, (Psalms 104:20) “[Thou makest darkness and it is night], wherein all the beasts of the forest creep forth”.

And take a bunch of hyssop, and dip it in the blood that is in the basin, and touch with it the lintel and the two side posts, with the blood that is in the basin; and none of you shall go out at the door of his house until the morning.

וּלְקַחְתֶּ֞ם אֲגֻדַּ֣ת אֵז֗וֹב וּטְבַלְתֶּם֮ בַּדָּ֣ם אֲשֶׁר־בַּסַּף֒ וְהִגַּעְתֶּ֤ם אֶל־הַמַּשְׁקוֹף֙ וְאֶל־שְׁתֵּ֣י הַמְּזוּזֹ֔ת מִן־הַדָּ֖ם אֲשֶׁ֣ר בַּסָּ֑ף וְאַתֶּ֗ם לֹ֥א תֵצְא֛וּ אִ֥ישׁ מִפֶּֽתַח־בֵּית֖וֹ עַד־בֹּֽקֶר׃