In Sūrat Hūd, āyah 69, When angels visiting Prophet Ibrāhīm (Abraham) ﷺ:

﴿ قالُوا سَلامًا قالَ سَلامٌ ﴾
“They said: salāman. He said: salāmun.”

The angels (disguised as guests) greet Ibrāhīm with peace, and Ibrāhīm greets them back. Simple on the surface — but look at the endings of the two “salām” words. They’re different on purpose.

The two endings : Why “rafʿ-vs-naṣb” difference 

The angels said: “salām‑AN” (naṣb / the “‑an” ending)

• Remember: naṣb has a hidden verb behind it.
• The full meaning is: “nusallimu salāman” → “We send a greeting of peace.”
• It describes an action they are doing — a greeting happening in that moment.

Ibrāhīm replied: “salām‑UN” (rafʿ / the “‑u” ending)

• Remember: rafʿ is a nominal sentence — no verb.
• The meaning is: “salāmun ʿalaykum” → “Peace [be upon you]” — peace as a standing, settled fact.
• No hidden “I send” — it just sits there as something permanent and established.

Why this matters — 

So when Ibrāhīm switched from the angels’ naṣb to his own rafʿ, he wasn’t just copying their greeting back — he upgraded it.

• The angels offered: “we greet you with peace” (an action, a moment).
• Ibrāhīm answered: “peace — settled, permanent, upon you” (a lasting state).

That’s why the scholars say: Ibrāhīm returned a better greeting than the one he received. And the Qur’an actually commands this elsewhere: ﴿وَإذا حُيِّيتُمْ بِتَحِيَّةٍ فَحَيُّوا بِأَحْسَنَ مِنْها أَوْ رُدُّوها﴾ — “When you are greeted with a greeting, respond with a better one, or [at least] return it” (al-Nisāʾ 4:86). Ibrāhīm did the “better one” — and he did it purely through grammar, by choosing rafʿ over naṣb