Praise of generosity, condemnation of miserliness, courage, separation and longing recur across Arabic poetry. Such general purposes belong to the shared expressive tradition and are not owned by one poet.
If two poets liken a brave man to a lion, that familiar analogy does not by itself establish borrowing. The resemblance between bravery and the lion is widely recognized.
A more serious question arises when an unusual image, its arrangement and its distinctive conclusion all reappear in a later composition. The likeness has then moved beyond a general theme.