Hadith #5198 (Sunan Abi Dawud)
Book: General Behavior (Kitab Al-Adab)
Narrator(s): Abdullah bin Wahb عبد الله بن وهب بن مسلم القرشي, Abu Hurairah, Abu Maryam al-Ansari أبو مريم الأنصاري, Ahmed bin Sa'id bin Sakhar أحمد بن سعيد بن صخر, Mu'awiya bin Salah bin Hadayr معاوية بن صالح بن حدير
Grade: Sahih

The young should salute the old, the one who is passing by should salute the one who is sitting, and a small company should salute a large one.

Source: https://parallelquran.com/hadith/sunan-abi-dawud-5198/