The mother of Imaam Abu Hanifah (rahimahullah) once needed to enquire regarding a certain mas’alah. She thus instructed Imaam Abu Hanifah (rahimahullah) saying, “Go to ‘Umar bin Zar and ask him regarding this mas’alah.” As Imaam Abu Hanifah (rahimahullah) knew the answer to the mas’alah, he told it to her. His mother, however, did not accept his answer and insisted that he go to ‘Umar bin Zar and ask him the question. Imaam Abu Hanifah (rahimahullah) therefore went to ‘Umar bin Zar and said, “My mother is in such-and-such a predicament and has told me to ask you the ruling regarding this situation.” On hearing this, ‘Umar bin Zar was extremely surprised and exclaimed, “You are asking me the mas’alah?” In response, Imaam Abu Hanifah (rahimahullah) replied, “My mother instructed me to ask you the mas’alah.” ‘Umar bin Zar did not know the answer to the question and thus said to Imaam Abu Hanifah (rahimahullah), “Tell me the answer so that I may tell it back to you.” Imaam Abu Hanifah (rahimahullah) therefore told ‘Umar bin Zar the answer after which ‘Umar bin Zar repeated it back to him. Imaam Abu Hanifah (rahimahullah) thereafter returned to his home and informed his mother of the answer of ‘Umar bin Zar.

(‘Uqoodul Jummaan pg. 272)