It is contrary to what is proper, and against the opinion of to partake of medicine by guess and to go after a caravan without seeing the road. The Imam Murshid Muhammad Ghazali, upon whom be the mercy of Allah, having been asked in what manner he had attained such a degree of knowledge, replied: ‘By not being ashamed to ask about things I did not know.’

The hope of recovery is according to reason,
That he should feel thy pulse who knows thy nature.
Ask what thou knowest not; for the trouble of asking
Will indicate to thee the way to the dignity of knowledge.

Saadi Shirazi

http://www.poemhunter.com/poem/ch-08-on-rules-for-conduct-in-life-maxim-54/