Rashi on Exodus 12:22/רש"י על שמות י״ב:כ״ב

1אזוב HYSSOP — a kind of herb which has thin stalks.

2אגדת אזוב A BUNCH OF HYSSOP — three stalks are called a bunch (cf. Shabbat 109b; Sukkah 13a).

3אשר בסף means WHICH IS IN THE VESSEL, as in (2 Kings 12:14) “basins (ספות) of silver.”

4מן 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).

5ואתם 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”.