Kitāb al-Ghayba

Hadith 380
imam-mahditwelve-imams
وأما من قال لا ولد لأبي محمد عليه السلام فقوله يبطل بما دللنا عليه من إمامة الاثني عشر وسياقة الأمر فيهم. ويزيده بيانا:
As for the assertion that Imam Hasan Askari (a.s) did not have a son, it is invalid, because we proved that the Imams are twelve and this divinely ordained authority is bestowed to them. There are some more reports on this topic, which we mention below:
Source: Shaykh Muḥammad b. al-Ḥasan al-Ṭūsī