Kitāb al-Ghayba > Refutation of all sects, which believed in Imamate of someone other than Master of the Age (a.s)
Hadith #3

وأما من قال إنه لا ولد لأبي محمد عليه السلام ولكن هاهنا حمل مشهور سيولد، فقوله باطل لأن هذا يؤدي إلى خلو الزمان من إمام يرجع إليه، وقد بينا فساد ذلك. على أنا سندل على أنه قد ولد له ولد معروف ونذكر الروايات في ذلك فيبطل قول هؤلاء أيضا.

As for the saying that Abu Muhammad did not have any offspring and that there is a hidden conceived baby, who will be born: It is invalid, because this suggests that this age is devoid of an Imam of guidance and we have demonstrated the falsity of this. Additionally, we will demonstrate that he sired a famous son and we will mention the traditions with that respect, which will invalidate this assertion as well.