Increase of Imaan

It was affirmed that Ammar Ibn Yasir said: 

"Three characteristics lead anyone who possesses them to have true Iman: to be just to oneself, to spend in spite of poverty, and to offer greetings to everybody [to those you know and to those you do not know]." 

Al-Bukhari recorded this in his Sahih. Also, Jundub Ibn Abd Allah, Ibn Umar, and others said: 

"We learned Iman, then we learned the Quran, and in turn increased our Iman."

Taken from the Increase and Decrease of Imaan by Shaykh ul-Islaam Ibn Taymiyyah (Kitaab ul-Imaan)