بسم الله الرحمن الرحيم
In the following hadith, Imams al-Sadiq (as) exposes the lies told by Ahmad al-Hassan, that there will be more than 12 Imams (as), Imam al-Sadiq (as) was asked about the number of Imams (as), and he (as) answered:
فقلت: أخبرني بعدتكم
فقال: نحن اثنا عشر هكذا حول عرش ربنا جل وعز في مبتدأ خلقنا، أولنا محمد، وأوسطنا محمد، وآخرنا محمد
[...] I said [to the Imam]: "Tell me about your number." He (as) said: "We are Twelve, and from the very beginning of our creation we were near to the throne of our Lord - the Magnificent and Almighty -. The first of us is Muhammad, the middle of us is Muhammad, and the last of us is Muhammad."
Source: Kitāb al-G̲h̲ayba byan-Numani, page 57, Hadith # 37
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