[Rashi says that the oath “not to force the end” prohibits excessive prayer. In Siman 24 the Rebbe asked how much is too much. In this siman he brings two places where the Yismach Moshe discusses this.

One Must Have a Rebbe
Don’t Be a Blind Follower
The Danger of Heretical Thoughts
Make Clear What You’re Protesting Against

Brisker Rav and Chazon Ish on the Oaths
When Excessive Prayer Becomes Permitted
Two Reasons Why We Eat Matza