"I am who I am, and my counsel is not with the wicked, but in the law of the Lord is my will"

"Ego et sum qui sum, et consilium meum non est cum impiis, sed in lege Domini voluntas mea est, alleluja."

     Currently antiphon to Ps 1, Office of readings for the Second Sunday of Easter/Divine Mercy Sunday (only?), though all (?) of the occurrences of this in the Cantus database are associated with the Mass.  Liturgy of the hours:  "I am who I am, and wicked men do not accept my ways, for the law of the Lord is my delight"; Universalis:  "I am who I am, and wicked men do not understand my ways:  my delight is the law of the Lord."  The earliest occurrence of this antiphon in Cantus at the moment (Albi, Bibliothèque municipale Rochegude, 44 (F-Al 44), 91r.) is dated c. 890, though the image is taken from the late 10th-century Sankt Gallen, Stiftsbibliothek, 391 (CH-SGs 391), 32.  A quick and dirty initial stab at potential sources (though I have not run lemma searches):

• "Ego et sum qui sum":  Ex 3:14.
• "consilium meum": see also the two entries below.
  
• "cum impiis":  Ps 25:5 ("with the wicked [(cum impiis)] I will not sit") and 9 ("with the wicked [(cum impiis)"), but more importantly Ps 1:1:  "Blessed is the man who hath not walked in the counsel of the ungodly [(in consilio impiorum)]".
• "sed in lege Domini voluntas mea est":  Ps 1:2:  "But his will is in the law of the Lord [(sed in lege Domini voluntas ejus)]", but also Is 46:10:  "My counsel shall stand [(Consilium meum stabit)]" and Lk 22:42:  "but yet not my will, but thine be done [(verumtamen non mea voluntas, sed tua fiat)]."