What is the ruling on swearing by the verses of Allah or by the Mus'haf, and is one permissible without the other? And does the saying "Cows do not butt with their horns" imply mockery of Hajj?

This saying is intended to express impossibility, like the impossibility of cows performing Hajj on their horns, and it does not mock Hajj. It is better to abandon it to prevent misunderstanding. There is a similar expression, such as the saying: "He will not submit until الخطاب's donkey submits," which was a phrase uttered by some Companions and approved by scholars without objection. This phrase does not disparage Islam but rather exemplifies the impossibility of 'Umar's conversion to Islam.