كتاب المقدمات
The Book of Miscellany
(7)
Chapter: Firm Belief and Perfect Reliance on Allah
(7)
- باب اليقين والتوكل
Riyad as-Salihin 76
Ibn 'Abbas (May Allah be pleased with them) said:
When (Prophet) Ibrahim (Abraham) was thrown into the fire, he said: "Allah (Alone) is sufficient for us, and, He is the Best Disposer of affairs." So did Messenger of Allah Muhammad (ﷺ) when he was told: "A great army of the pagans had gathered against him, so fear them". But this (warning) only increased him and the Muslims in Faith and they said: "Allah (Alone) is sufficient for us, and He is the Best Disposer of affairs (for us)".

[Al-Bukhari].

الثالث‏:‏ عن ابن عباس رضي الله عنهما أيضاً قال‏:‏ ‏"‏حسبنا الله ونعم الوكيل، قالها إبراهيم صلى الله عليه وسلم حين ألقي في النار، وقالها محمد صلى الله عليه وسلم حين قالوا‏:‏ إن الناس قد جمعوا لكم فاخشوهم فزادهم إيمانا وقالوا‏:‏ حسبنا الله ونعم الوكيل‏:‏ ‏(‏‏(‏رواه البخاري‏)‏‏)‏‏.‏
Reference : Riyad as-Salihin 76
In-book reference : Introduction, Hadith 76