Is it permissible to initiate greeting a non-Muslim with a salutation other than "As-salamu alaykum," such as "Sabah al-khair" (Good morning), and did the majority of the Companions permit that?

What is forbidden is initiating greetings of peace with disbelievers, based on the hadith: "Do not initiate greetings of peace with Jews and Christians." As for addressing them with other phrases, such as "Good morning," it is permissible. There is no disagreement among the Companions regarding the permissibility of saying "Good morning" to disbelievers.