Al-Kāfi - Volume 1 > The Birth of the Imams (a.s.)
Hadith #3

3ـ مُحَمَّدُ بْنُ يَحْيَى عَنْ أَحْمَدَ بْنِ مُحَمَّدٍ عَنْ عَلِيِّ بْنِ حَدِيدٍ عَنْ مَنْصُورِ بْنِ يُونُسَ عَنْ يُونُسَ بْنِ ظَبْيَانَ قَالَ سَمِعْتُ أَبَا عَبْدِ الله (عَلَيْهِ السَّلام) يَقُولُ إِنَّ الله عَزَّ وَجَلَّ إِذَا أَرَادَ أَنْ يَخْلُقَ الامَامَ مِنَ الامَامِ بَعَثَ مَلَكاً فَأَخَذَ شَرْبَةً مِنْ مَاءٍ تَحْتَ الْعَرْشِ ثُمَّ أَوْقَعَهَا أَوْ دَفَعَهَا إِلَى الامَامِ فَشَرِبَهَا فَيَمْكُثُ فِي الرَّحِمِ أَرْبَعِينَ يَوْماً لا يَسْمَعُ الْكَلامَ ثُمَّ يَسْمَعُ الْكَلامَ بَعْدَ ذَلِكَ فَإِذَا وَضَعَتْهُ أُمُّهُ بَعَثَ الله إِلَيْهِ ذَلِكَ الْمَلَكَ الَّذِي أَخَذَ الشَّرْبَةَ فَكَتَبَ عَلَى عَضُدِهِ الايْمَنِ وَتَمَّتْ كَلِمَةُ رَبِّكَ صِدْقاً وَعَدْلاً لا مُبَدِّلَ لِكَلِماتِهِ فَإِذَا قَامَ بِهَذَا الامْرِ رَفَعَ الله لَهُ فِي كُلِّ بَلْدَةٍ مَنَاراً يَنْظُرُ بِهِ إِلَى أَعْمَالِ الْعِبَادِ.

3. Muhammad ibn Yahya has narrated from Ahmad ibn Muhammad from Ali ibn Hadidfrom Mansur ibn Yunus from Yunus ibn Zabyan who has said the following. “I heard abu ‘Abdallah (a.s.) say, ‘When Allah, the Most Majestic, the Most gracious, decides to create the Imam from another Imam He sends an angel with a drink of water from under the Throne. Then the angel would make the Imam to drink it and would give it to him to drink. For the first forty days he would not hear any words and thereafter he would hear words. When his mogthor would give birth Aallah would send the same angel who had brought the water. The angels would on his right should, “. .in all truth and justice, your Lord’s Word has been completed. No one can change His Words. He is All-hearing and All-knowing.”. (6:115) When he would rise to execute the task of an Imam Allah would raise a light house for him in every town through which he would examine the deeds of the servants of Allah.”