Rashi

האלהים מצא GOD HATH FOUND OUT — We know that we have done no wrong, but it has been brought about by the Holy One, blessed be He, that this should come upon us. The Creditor has found an opportunity to collect His debt (Genesis Rabbah 92:9). מה נצטדק How shall we justify ourselves? — This is a verbal form of צדק. In the same way every root whose first letter is צ when used in the Hithpael or Nithpael takes a ט instead of the ת of the prefix. This, however, is not placed before the first radical letter, but between the first two letters of the root. For example: נצטדק of the root צדק; (Daniel 4:13) “and let it be wet (ויצטבע)” of the root צבע to steep; Joshua 9:4) “and made as if they had been ambassadors (ויצטירו)”, of the same root as ציר in (Proverbs 13:17), ציר אמונים a faithful ambassador”; (Joshua 9:12) “we took our provision (הצטידנו)” of the same root as צדה in (Genesis 45:21) צדה לדרך “provision for the way”. And in the same way, with a root whose first letter is ס or ש, when it is used in the Hithpael, the ת of the prefix separate (i.e. is placed between) the first two letters of the root. For example: (Ecclesiastes 12:5) “and the grasshopper shall drag itself along heavily (ויסתבל)” from the root סבל “to carry a load”; (Daniel 7:8) “I considered (משתכל הוית) the horns”, from the root שכל to reflect on: (Micah 6:16) “for the statutes of Omri are kept (ישתמרו)” from the root שמר to keep; (Isaiah 59:15) “And he that departeth from evil (משתולל) is regarded as a fool”, from the same root as שולל in (Job 12:17) “He leadeth counsellors away (שולל) as though they were fools”; (Exodus 9:17) “Thou treadest down (מסתולל) my people”, from the same root as סלולה in (Jeremiah 18:15) “a way not trodden down (סלולה).”