There are not many poems about "rationality", but there are many sentences describing "rationality". Here are five examples:
Poetry is mature rationality. German playwright, poet, and thinker Goethe
Irrational does not necessarily mean irrational. Reasonable Quotes by British political historian Lewis Namier
Reason is the compass, desire is the storm. Austrian philosopher Karl Popper
The first norm of reason is the law of nature. German writer Kampis
All rational animals will be bored.
Russian poet Pushkin