Poetry has its own rhyme system, but poets may also arrange matching sounds within a single couplet. This motivates discussion of a sajʿ-like effect in verse.
Parts of the verse may echo each other while the poetic meter remains intact. This creates inner sound correspondence in addition to the ordinary final rhyme.
Prose sajʿ and poetic rhyme should not be collapsed. A couplet’s final rhyme and its internal sound pattern are two different levels; a particular structured form is known as tashṭīr.