פירוש על סנהדרין 33:3

"and they will cease on their own" -- the interpretation is that their prophecy will cease, because the Shechinah does not descend in the midst of sadness, but rather in the midst of joy.

From the mouth of the interpreter: So that when foreign-speaking witnesses came to testify before them, they did not have to contend with the doubters among them that this was hearsay.