I have always found lions to be a majestic creature, very powerful and brave. In many Islamic countries lions seem to be respected too (For example; the nickname of the Iraqi football team is 'Mesopotamian Lions', and Morocco 'Lions of the Atlas'). My questions is:
Are lions mentioned in the Qur'an or any other Islamic source, and if so, are they positively mentioned?
There is one verse of the Qur'an that mentions lions specifically, but it uses an unusual word (قسورة rather than either ليث or أسد). It is used in Surah Muddathir:
So it is describing that a lion is an animal to be feared, with the rejecting non-Muslims fleeing from the message, like donkeys fleeing from a lion.
In the hadith there are many mentions of lions. In particular, the Prophet's uncle Hamza ibn Abd Muttalib had the title of the Lion of Allah (أسد الله) according to wikipedia. Clearly, this is in the context of Hamza being amazingly brave; so it is being used in the sense you refer to it.
There's an other synonym of Lion أسد mentioned in the Qur'an in one of the last revelations Verse (5:3).
Prohibited to you are dead animals, ..., and those from which a wild animal has eaten ...
This is السَّبُعُ as-Sabu'u or السِباع as-Siba' which refers to any wild beast (like lions, tigers, "wild" dogs, birds of prey ...) or any animal which who has claws and attacks humans or brutes and jam them in general!
