If he greets people who are both awake and asleep, he should lower his voice so that those who are awake can hear him without waking those who are asleep. This is a refined Islamic etiquette. The Prophet (peace and blessings be upon him) would come at night and offer the greeting of peace in a manner that did not wake those who were asleep but could be heard by those who were awake. Muslim narrated this in his Sahih as part of a lengthy hadith1.

It is Sunnah to offer the greeting of peace before speaking, based on the hadith: “If someone begins speaking before offering the greeting of peace, do not respond to him.” Ibn al-Sunnī narrated it in The Day and Night’s Devotions2.

The more fully a Muslim uses the transmitted formulas of greeting, the greater his reward; each additional phrase earns him ten good deeds. Abū Dāwūd and al-Tirmidhī narrated from Imrān ibn Husayn (may Allah be pleased with him): “A man came to the Prophet (peace and blessings be upon him) and said, ‘Peace be upon you.’ He returned his greeting, and the man sat down. The Prophet then said, ‘Ten.’ Another man came and said, ‘Peace be upon you and the mercy of Allah.’ He returned his greeting, and the man sat down. The Prophet then said, ‘Twenty.’ Another man came and said, ‘Peace be upon you, and the mercy and blessings of Allah.’ He returned his greeting, and the man sat down. The Prophet then said, ‘Thirty.’”3.

A Muslim should not add anything beyond this, such as saying, “and His forgiveness and good pleasure,” because the prescribed greeting ends with “and His blessings.” Had there been any good in adding to it, the Messenger of Allah (peace and blessings be upon him) would have directed us to it. Mālik narrated in al-Muwattaʾ from Muhammad ibn Amr ibn Atāʾ, who said: “I was sitting with Abd Allah ibn Abbās (may Allah be pleased with him and his father) when a man from Yemen entered and said, ‘Peace be upon you, and the mercy and blessings of Allah.’ He then added something else as well,