As evidence for his first claim...
As evidence for his first claim, Ibn Taymiyyah mentions only Imam al-Tabari and Ibn Qani’ by name. Then, he makes a vague reference to some other Sunni scholars of geneology and history. Imam al-Dhahabi (d. 748 H) quotes something to this effect too: قلت: ويزعمون أن محمدا دخل سردابا في بيت أبيه، وأمه تنظر إليه، فلم يخرج إلى الساعة منه، وكان ابن تسع سنين. وقيل دون ذلك ...
وأنه حي نعوذ بالله من زوال العقل ….وممن قال: إن الحسن العسكري لم يعقب: محمد بن جرير الطبري، ويحيى بن صاعد، وناهيك بهما معرفة وثقة. I (al-Dhahabi) say: They (the Shi’ah) claim that Muhammad entered a cellar in the house of his father while his mother was looking at him, and has not come out from it up till this moment, and he was nine years old. It is said that his age was other than that ... And that he is alive. We seek the refuge of Allah from the dysfunction of the intellect....
Among those who said that al-Hasan al-Askari did not have a child were Muhammad b. Jarir al-Tabari and Yahya b. Sa’id, and they are sufficient for you in knowledge and trustworthiness .[^2] However, it seems that al-Dhahabi himself did not attach much weight to the submissions of al-Tabari, Ibn al-Qani’, Yahya b. Sa’id, Ibn Taymiyyah (who was his contemporary) and probably others.
al-Harith al-Baghdadi, Ibrahim b. Hani al-Naysaburi, Sa’dan b. Nasr, Salih b. Ahmad b. Hanbal, ‘Abd Allah b. Muhammad b. Ayub al-Mukhrami, ‘Ali b. Harb al-Tai, Abu Hafs al-Naysaburi al-Zaid ‘Umar b. Salam, Muhammad b. al-Hasan al-‘Askari from the Twelve (Imams ), Muhammad b. Harun al-Falas, and Harun b. Sulayman al-Isbahani.[^3] So, al-Dhahabi personally believed that Imam al-Askari had a son named Muhammad, but who allegedly “died” in 265 H.
He did not accept the apparently hearsay testimonies of al-Tabari and similar Sunni scholars, despite affirming their scholarship and trustworthiness. The reason, perhaps, is that none of them was an eye-witness to the alleged incidents, and none of them ever mentioned any source for his information.