https://wowwiki.fandom.com/wiki/Procs_per_minute
PPM and Haste
The speed used for calculating the PPH (Proc Per Hit) chance is the basic weapon speed, not the characters haste-affected hit speed. This means the probability of a proc is not lowered or increased by haste. What haste does is increase the total amount of melee hits per time and thus the total amount of procs.