Kitāb al-Ghayba

Hadith 121
occultationimam-kazimahl-al-baytimam-mahdi
61- قال: وروى علي بن معاذ قال: قلت لصفوان بن يحيى: بأي شي‏ء قطعت على علي؟قال: صليت ودعوت الله واستخرت عليه وقطعت عليه.
H 61 - Ali bin Maaz narrated: I asked Safwan bin Yahya: Through which reasoning have you adopted faith in the Imamate of Imam Musa Kadhim (a.s)? He replied: I prayed the ritual prayer and after that sought counsel (Istikhara) from Almighty Allah and the result was that I got certainty about it.
Source: Shaykh Muḥammad b. al-Ḥasan al-Ṭūsī