Kommentar zu Divrej Hajamim II 23:5

And a third shall be in the king’s palace to guard that they would not gather about him to assassinate him.

and a third This is the second one.

in the Yesod Gate But in II Kings (ad loc.) it is written “the Sur Gate.” In Yoma Yerushalmi (in extant editions it is found in Erubin Yerushalmi 5:1) it is explained that the Yesod Gate had seven names: 1) the Sur Gate, because they would purify those smitten with zaraath there [by placing the blood of the guilt offering and the oil] on their thumbs, reminiscent of [the verse] (Lam. 4:15): “They called out to them: ‘Depart (סוּרוּ), unclean [ones]!’”