Wa alaykum salaam Muntazir
My proof is not from Hadith or from the Qur'an. It is simply from the definition of the English word 'Poetry'.
po·em (pō'əm)
n.
1. A verbal composition designed to convey experiences, ideas, or emotions in a vivid and imaginative way, characterized by the use of language chosen for its sound and suggestive power and by the use of literary techniques such as meter, metaphor, and rhyme.
2. A composition in verse rather than in prose.
3. A literary composition written with an intensity or beauty of language more characteristic of poetry than of prose....
Source:
http://www.answers.com
and
po·et·ry (pō'ĭ-trē)
n.
...
3. A piece of literature written in meter; verse.
4. Prose that resembles a poem in some respect, as in form or sound...
6. A quality that suggests poetry, as in grace, beauty, or harmony....
You must have noticed while reading the Qur'an in Arabic that Allah (swt) uses many metaphors. The Qur'an is written in verses (a charachteristic of poetry) and not in paragraphs (as in prose). Also in many Surahs, all the words in the end of the verses rhyme with each other, which is again poetic.
umm...you seem to have a point asking this. Is it because of the verse in suratul Yasin saying 'wa ma 'alamnahush shi'ra..."? If you are, I checked the commentary of the verse and it says
'Poetry' here means proposition based on imaginary data exciting human emotions.
(commentary by Ayatullah Agha H.M.M. Pooya Yazdi and S.V. Mir Ahmed Ali)
I hope that explanation is ok...
If Allah assists you, there is none that can overcome you; and if He forsakes you, then who is there that can assist you after Him? And on Allah should the believers rely (Qur'an 3:160)