Reference : Hisn al-Muslim 225

ثَلاَثٌ مَنْ جَمَعَهُنَّ فَقَدْ جَمَعَ الْإِيمَانَ: الْإِنْصَافُ مِنْ نَفْسِكَ، وَبَذْلُ السَّلاَمِ لِلْعَالَمِ، وَالْإِنْفَاقُ مِنَ الإِقْتَارِ
Three characteristics, whoever combines them, has completed his faith: to be just, to spread greetings to all people and to spend (charitably) out of the little you have.

Reference:
Al-Bukhari, cf. Al-Asqalani, Fathul-Bari 1/82 as a statement of the 
Companion 'Ammar (RA).

Chapter: Excellence of spreading the Islamic greeting