I told you once before
I ain't rapping too fast, y'all just listening too slow

from Kendrick Lamar (Ft. DJ Quik, E-40, Kurupt, Snoop Dogg, Xzibit & YG) – BET Cypher 2012: The West Coast Lyrics on Rap Genius

Actually, E-40 has said this multiple times:

In case you suckers didn’t know, I told you once before
I ain’t rapping too fast, see y'all just listening too slow
– Fallin' Rain

And once more after that:

And oh yeah, just to let you suckers know
I ain’t rapping to fast y'all just listening too slow
– Fuck Em

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