Kitāb al-Ghayba 1, narration 40

Translation

However, since his obedience is obligatory in the present, and we do not find obedience to him to be stipulated with any condition or a specific time, it follows that he must be existent, so the legitimate excuse of the divinely ordained duties is removed and such duties become fair. The response to the example of the master and his slave is the same, because he ordered his servant to approach him at present, not to buy. And when he approaches him and he requires him to buy, he must give him the money. That is why we said that Allah, the Exalted, has set obligations for all who will come until Judgment Day, and it is not necessary that they should be existent and without legitimate excuses, for He has not set obligations over them now; when He creates them and removes their excuses with respect to the duties by granting them power and instruments and setting proofs, then the duties will be imposed on them. In this way, the misunderstanding of our opponent regarding the existence of the Imam is rendered invalid.

Translation: Sayyid Athar Husain S. H. Rizvi — published with the edition, reproduced verbatim.