The Messenger of Allah ﷺ said, "Successful is the one who has submitted, been granted enough to suffice him, and been made content by Allah with what He has given him."
حدثنا عبد الله بن يزيد المقرئ من كتابه حدثنا سعيد بن أبي أيوب حدثني شرحبيل بن شريك عن أبي عبد الرحمن الحبلي
أن رسول الله ﷺ قال قد أفلح من أسلم ورزق كفافا وقنعه الله بما آتاه
Its isnad is sahih. Muslim (1:287) and Tirmidhi (3:270) both narrated it, both by way of Abdullah bin Yazid, the teacher of Ahmad here, with this same isnad. Tirmidhi said, a hasan sahih hadith. Ibn Majah (2:277-278) narrated it by way of Ubaydullah bin Jafar and Humayd bin Hani, from Abu Abdul-Rahman Hubli, with similar wording. Abu Naeem narrated it in Hilya (6:129) through the narration of Abdul-Rahman bin Salama Jumahi, from Abdullah bin Amr.Al-kafaf, with the fatha on the kaf, refers to that which does not exceed what is needed, but is only enough to meet one's need.