Kitāb al-Ghayba > Concealed Birth of the Imam of the Time (a.s) was not an extraordinary event
Hadith #11

وقد سبق الخبر عن آبائه عليه السلام بأن القائم عليه السلام له غيبتان؛أخراهما أطول من الأولى. فالأولى يعرف فيها خبره،والأخرى لا يعرف فيها خبره. فجاء ذلك موافقا لهذه الأخبار فكان ذلك دليلا ينضاف إلى ما ذكرناه وسنوضح عن هذه الطريقة فيما بعد إن شاء الله تعالى. فأما خروج ذلك عن العادات، فليس الأمر على ما قالوه،ولو صح لجاز أن ينقض الله تعالى العادة في ستر شخص ويخفى أمره لضرب من المصلحة وحسن التدبير لما يعرض من المانع من ظهوره.

Narrations from his holy forefathers (a.s) had preceded him that the Qaim (a.s) will have two occultations, one of which is longer than the other; and that in the first, communication with him will be established and in the second, it will not be. The events unfolded as predicted by these narrations, enhancing the strength of our arguments. We will explain this reasoning in the future, God willing. This is not an event so out of the ordinary, as they have suggested. Even if it were so, it is reasonable that Allah may violate the ordinary in the case of hiding a specific person and to conceal him, because it is expedient and wise.