Abu Yusuf relates the invocation principally to the opening of prayer, for seeking protection at its beginning. Muhammad regards it as attached especially to Quranic recitation, drawing on the wording of Quran 16:98.
This distinction matters for the follower because in Hanafi law the follower does not undertake independent Quranic recitation. The disagreement is about the occasion and legal connection, not whether refuge is a sanctioned invocation.