Must one specify that a fast (Ramadan, make-up, expiation, or vow) is obligatory when forming the intention?

Primary text

When specifying the intention for a fast such as Ramadan, its make-up, expiation, or a vow, it is not required to specify that it is obligatory. This ruling aligns with the view of Imam Ahmad. This is analogous to the ruling on prayer intention, as previously established.