Sayyiduna Jabir bin Abdullah (may Allah be pleased with them both) said that he performed the fear prayer with the Prophet (peace and blessings be upon him). At the end of this hadith it says: He (peace and blessings be upon him) gave the salam and we all gave the salam. Sayyiduna Jabir (may Allah be pleased with them both) said: Your royal guards used to do the same with their commanders.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب صلاة الخوف / 6027