Jinās compares individual word forms, wherever they appear in a passage. Sajʿ compares the terminal expressions of distinct prose clauses. A vague rhyming impression therefore does not establish sajʿ.
If similar forms occur within a clause, the question may chiefly concern jinās. If corresponding sounds occupy the ends of two complete clauses, the conditions of sajʿ become relevant. Both may occur together, but each needs a separate demonstration.
The highest standard of sajʿ is that sound serves meaning. When clauses are distorted merely to secure a rhyme, the device may remain present yet become rhetorically less effective.