Clear declaration of Imam Kadhim about the Imamate of Imam Ridha
Kitāb al-Ghayba|Volume 1|Book 1|Chapter 10
23- وفي خبر آخر قال أبو عبد الله عليه السلام في حديث طويل: يظهر صاحبنا وهو من صلب هذا، وأومأ بيده إلى موسى بن جعفر عليه السلام، فيملأها عدلا كما ملئت جورا وظلما وتصفو له الدنيا.
H 23 - In another report, Abu Abdullah عليه السلام said in a lengthy tradition: Our master will appear from his loins; and he pointed to Imam Musa Kadhim عليه السلام. Thus, he would fill up the earth with justice and oppression as it would have been filled with injustice and tyranny; and the world would be cleaned and prepared for him.