“Ibn Jawzi” writes in his book:

“کان أبو بکر وعمر یشاورانه ویرجعان إلى رأیه، وکان کل الصحابة مفتقرا إلى علمه، وکان عمر یقول: أعوذ باللَّه من معضلة لیس لها أبو الحسن”

“Abu-Bakr” and “Umar” would consult with hadrat “Ali” and would refer to his opinion and all the companions needed his knowledge and “Umar” would say: I refuge to god from {scientific} problems that “Abu al-Hassan” {commander of the faithful} isn’t there to answer them.

“Al-Muntazam fi Tarikh al-Umam wa al-Mulouk” – vol. 5, p 68