Source: Shaheed Murtada Mutahhari, The Narrative of Veracious, Vol.1, STORY NO.20, p.49-50
Abu ‘All ibn Sinâ was not even twenty years old when he came to know the sciences of his time. He was ranked in the highest place in theology, natural sciences, mathematics and religious studies during his period. He attended the session course of Maskuyeh the renowned scholar of that period.
With an utmost arrogant way, he threw a walnut in front of Ibn Maskuyeh and said: “Determine its surface?
Ibn Maskuyeh placed a few phamphlets before Ibn Sinã related to ethics and education from the book—” Taharat ul-A’raq”—and said: ‘First of all, reform your behaviour and conduct till I determine the surface of walnut. You are in more need of your ethical amendment rather than me to determine the surface of this walnut.”
Abü ‘All, on hearing this remark, felt shy and disgraceful. These words were of great use to him throughout his life.1

NOTES
1. History of Rational Sciences in Islam, p. 211.