Sayyiduna Umar bin al-Khattab (may Allah be pleased with him) narrates: The Prophet (peace and blessings be upon him) said: "When two Muslim men meet and one of them greets the other with salam, the more beloved of the two to Allah Almighty is the one who meets the other with the more cheerful face. And when the two shake hands, one hundred mercies descend upon them; the one of them who took the initiative receives ninety (mercies), and the one who shakes hands (in response) receives ten (mercies)."
Al-Bazzar recorded it, and its chain contains a narrator whom I do not know.
Hadith Referenceمجمع الزوائد ومنبع الفوائد / كتاب الأدب / 12767