I once got angry with my son; so I told him, "if I ever ask you to get married again, it will be like asking you to marry me." I just told him that without swearing by Allah.
What is the Kaffarah (expiation) in this case?
The manner in which you uttered your words in the question is not considered an oath. Hence, there is no Kaffarah or any sort of compensation that you have to do. Also, there is no harm in you asking your son to marry in the future, because this urges him to observe his chastity. It is preferable that you avoid using such bad phrases (Part No. 23; Page No. 193) that may entail violating a Shari`ah (Islamic law) ruling if you do otherwise or likening lawful and permissible things to what is prohibited under the Shari`ah.May Allah grant us success. May peace and blessings be upon our Prophet Muhammad, his family, and Companions.