It is reported that Al-Hasan Al-Basrî – Allâh have mercy on him – said when asked ‘what is îmân (faith)?’:

It is perseverance (al-sabr) from the things that are forbidden by Allâh the Mighty and Majestic and acceptance. He was asked, “What is perseverance and acceptance?” He replied, “al-sabr is to persevere in holding back from what Allâh has forbidden, and [acceptance is] acceptance of what Allâh the Mighty and Majestic has commanded.”

Abû Bakr Al-Daynûrî, Al-Mujâlasah wa Jawâhir Al-‘Ilm 3:535.