أَوْفَى زَيْدٌ بِعَهْدِهِ. الْوَفَاءُ خُلُقُ الْكِرَامِ.
Zayd fulfilled his promise. Fidelity is a virtue of honorable people.
The first clause reports a particular event; the second supports it with a more general maxim. This is a plausible tadhyīl, since an independent assertion embraces and reinforces the preceding meaning.
If the second merely restated 'Zayd kept his promise' in near-identical terms, repetition would be more salient. Tadhyīl adds a separately phrased confirming principle.