It is narrated from the eighth Shia Imam, Ali ibn Musa Al-Ridha/Reza (AS) who said:

No one was wiser than my father (seventh Shia Imam, Musa Kadhim (AS)). In spite of that, Imam (AS) sometimes used to consult (ask for advice) with a black slave. When others protested about consulting with a black slave, Imam (AS) replied: Perhaps (maybe), Allah (SWT) placed the correct opinion on his tongue [1]. Of course, the subject and the experience and the qualification of the person who is consulted are the main elements to be considered when consulting others.

[1] Makaremul Akhlaq, Vol. 2, Page 99.

Source: en.shafaqna.com