Al-Matalib al-'Aliyah 2697 — The greeting of salam

Zayd bin Aslam (may Allah have mercy on him) relates: My father sent me to Sayyiduna Abdullah bin Umar (may Allah be pleased with them both), and I entered upon him (inside his house) without asking permission. (Zayd says that) he said, teaching me (the etiquette of social conduct): "When you wish to enter, first ask permission; then, if you are given permission, give the greeting of salam and enter." (Then Ibn Umar (may Allah be pleased with him)) asked: What do you need? I said: My father has sent me to you with the request that you write for him the price of your share at Khaybar in exchange for aqit (dried curd). So he wrote that for him and asked: Did you stop (on hearing the instruction)? I said: Yes.
The chain of this report is sahih (authentic), and all its narrators are thiqat (trustworthy) and reliable.