الكافي 1/4/75/12

12. Ali ibn Muhammad has narrated from Ishaq ibn Muhammad from Shahwayh ibn ‘Abdallah al-Jallab who has said the following. “Abu al-Hassan wrote to me in a letter as herein below. “You wanted to ask about the succeeding Imam after (the death) of abu Ja‘far and you were anxious about it. Do not feel sad; “God does not misguide a nation after having given them guidance until the means of piety are made known to them. . .” (9:115) Allah, the Most Majestic, the Most gracious, does not neglect the people whom He has granted guidance to go astray until He clarifies for them the means with which they can maintain piety. You master (Imam) after me will be, my son, abu Muhammad عليه السلام . With there is whatever you would need. Allah allows to precede whatever He wants and Allah allows to succeed whatever He wants. “For whatever sign We change or eliminate or cause to recede into oblivion, We bring forth a better sign, one that is identical.. .” (2:106) . I have written enough convincing facts for the people of reason with awareness.”