Sahih Bukhari
Oaths and Vows
Volume: 008 / Book Number: 078 / Hadith Number: 651
Narrated Haritha bin Wahb:
I heard the Prophet saying, "Shall I tell you of the people of Paradise? They comprise every poor humble person, and if he swears by Allah to do something, Allah will fulfill it; while the people of the fire comprise every violent, cruel arrogant person."