A man from Mā Warā’ Nahr Balkh (Transoxania) came to Imām al-Ridā, peace be on him, and said to him: “I want to ask you a question. If your answer is the same as I have already known, I will believe in your Imāmate.”
“Ask whatever you like,” replied the Imām.
The man asked the Imām, saying: “Tell me about your Lord: Since when and how (in what state) has your Lord been in existence and what does He subsist on?”
“Verily, Allah, the Blessed and Exalted, determined the ‘where’ without ‘whereness’; and He fashioned the ‘how’ without ‘howness’; and He subsists on His own power,” replied the Imām.
Surely, it is Allah, the Most High, who created space and time; they are of His creatures; therefore, how is He described by them?
The man admired the Imām’s answer, and then he hurried to kiss his head and said: “I witness that there is no god but Allah, that Mohammed is the Messenger of Allah, that ‘Ali is the testamentary trustee of Allah’s Messenger and the custodian after him for what Allah’s Messenger (may Allah bless him and his family) had undertaken, that your are the true Imāms, and that you are the successor after them.”
The Imām was among the sources of guidance and light on earth, hence he spread in his time faith in Allah and established argument against the creatures. ( Usūl al-Kāfi, vol. 1, pp. 88)