1. Al-Laalikaaee reports, in Sharh Usool Itiqaad Ahlis-Sunnah (5/958/no.1737), that Abd ar-Razzaaq (as-Sanaanee) said, I met seventy Shaikhs, from amongst them are Mamar, al-Awzaaee, ath-Thawree, al-Waleed ibn Muhammad al-Quraashee, Yazeed ibn as-Saaib, Hammaad ibn Salamah, Hammaad ibn Zayd, Sufyaan ibn Uyainah, Shuayb ibn Harb, Wakee ibn al-Jarrah, Maalik ibn Anas, Ibn Abee Laylaa, Ismaeel ibn Ayyaash, al-Waleed ibn Muslim and those I have not named, all of them saying: Faith is saying and action, it increases and decreases.
Abdullah ibn Ahmad reports in as-Sunnah (no.612): My father narrated to me: Abu Salamah al-Khuzaaee related to us, saying, Maalik, Shareek, Abu Bakr ibn Ayyaash, Abdul-Azeez ibn Abee Salamah, Hammaad ibn Salamah and Hammaad ibn Zayd said, Faith is conviction, declaration and action.
Al-Laalikaaee reports (5/959/no.1740) that Uqbah ibn Alqamah said: I asked al-Awzaaee about Faith; can it increase? He said, Yes, until it becomes like the mountains. I said, Can it decrease? He said, Yes, even until nothing remains of it.
Amongst the verses quoted by the scholars as proof for the fact that faith increases are: Aayah 173 of Soorah Aali-Imraan, Aayah 4 of Soorah al-Fath and Aayah 124 of Soorah at-Tawbah.