In his book "Vaishnavism Its Philosophy, Theology and Religious Discipline" SM Srinivasa Chari (Motilal Banarsidass, 4th reprint, Delhi 2018) writes on page 141:
the other episode refers to Rudra, who was cursed by Brahma because of the offense committed to him by cutting off one of his four heads.
The usual rendering of the story is that Brahma started off with five heads and became Chaturmukha Brahma after Siva cut one of his heads off.
It is not clear what Mr. Chari's source is for his statement above.
