Is the prohibition against saying "Sabah al-khair" (Good morning) correct, on the pretext that the polytheists said it after the death of the Prophet, may God's prayers and peace be upon him?

There is no evidence that the polytheists said "Good morning" (صباح الخير) after the death of the Prophet, peace be upon him. They used to say "May your morning be pleasant" (أنعم صباحاً) before Islam, but then the Prophet, peace be upon him, forbade this greeting and replaced it with "peace" (السلام). The hadiths indicate a prohibition against greeting with the phrase "Good morning" (صباح الخير) if it comes as a substitute for "peace" (السلام). It is permissible to say "How have you become this morning?" (كيف أصبحت؟) or "How have you become this evening?" (كيف أمسيت؟) after the greeting of peace. If said before it, and it suffices, that is acceptable.