Where in Shakespeare's tragedy Othello does Iago compare himself to Satan?

Ironically, although Iago, near the beginning of
Othello, says that he hates the Moor as much as he hates
“hell-pains” (1.1.151; Signet Classic Shakespeare), he later
closely identifies himself with hell.  Thus, when falsely advising Roderigo later in the
play, Iago says,

readability="12">

If sanctimony and a frail vow betwixt an erring
barbarian [that is, Othello] and a supersubtle Venetian [that is, Desdemona] be not too
hard for my wits, and all the tribe of hell, thou [that is, Roderigo] shall enjoy her.
(1.3.349-51)

A little later
in the same scene, after Roderigo has departed, Iago announces that he has thought of a
way to deceive and destroy Othello:

readability="7">

I have’t! It is engendered! Hell and
night

Must bring this monstrous birth to the world’s light.
(1.3.392-93)

As is so often
in the case in so many of Iago’s speeches, practically every word in the quotations just
cited is ironic.  Thus, when he refers to “sanctimony,” or a sacred bond, he reminds us
of his own bond with Othello, which he plans to break. The words “frail vow” are ironic
for the same reason.  Iago, meanwhile, is in some ways much more an “erring barbarian”
than Othello is; he corrupts and perverts and abuses his reason, and he is far more of a
real outsider, far more of a truly uncivilized person, than Othello is. Similarly ironic
is “supersubtle” – a word that applies far more to Iago than to Desdemona.  Meanwhile,
little is ever “too hard” for Iago’s “wits,” but he has corrupted and perverted those
wits. By identifying himself with “all the tribe of hell,” Iago gives us an important
clue about his own personality and motives.  Likewise, when he later identifies himself
with “Hell and night,” his words are revealing, and indeed some critics seem him as
almost literally (not just figuratively) demonic.