פירוש על קידושין 36:6

The baraita discusses whether a father can sell his daughter to someone she may not marry. According to the first opinion, if the marriage would be a high level prohibition, punishable by karet or death, then he may not sell her to this man. But if it is a lower level prohibition, such as a divorcee to a Kohen, then he may. R. Eliezer says he always may sell her to a man whom she may not marry.