Bhagavad Gita, Chapter 6, Verse 25

With the intellect set in patience, with the mind fastened on the Self, let him attain quietude by degrees; let him not think of anything.

Slow and steady is named directly here, not as a consolation, but as the real, intended pace.

There's real reassurance built into this instruction. Progress isn't expected to be instant, gradual, sustained effort with genuine conviction is described as exactly the right way to get there, not a lesser substitute for a faster method.