Once Muawiyah came to Medina, met Imam Hasan (a.s) and asked, “You Bani Hashim claim that every dry and wet thing is mentioned in the Quran and you have the knowledge of all of them.” “Indeed,” said the Imam. Muawiyah said, “If it is so, tell me where is the mention of our beards in the Quran?” Now Imam Hasan (a.s) had a luxurious and thick facial growth while the beard of Muawiyah was scanty. “Why not!” said Imam (a.s), “Have you not read the verse of Quran:
And as for the good land, its vegetation springs forth (abundantly) by the permission of its Lord, and (as for) that which is inferior (its herbage) comes forth but scantily… (Surah Araaf 7:58).
There are subtle points in this and only those with a literary taste can appreciate them. It is sufficient if we can just realize how great was the Quranic knowledge of Imam Hasan (a.s).
Reference :Akhlaq al-A’imma, Morals & Manners of the Holy Imams