الذين قال لهم الناس إن الناس قد جمعوا لكم فاخشوهم فزادهم إيمانا
Those unto whom the people said, "Verily, the people have gathered against you, therefore, fear them.'' But it (only) increased them in faith,
it means, those who threatened the people, saying that the disbelievers have amassed against them, in order to instill fear in them, but this did not worry them, rather, they trusted in Allah and sought His help.
وقالوا حسبنا الله ونعم الوكيل
and they said: "Allah is Sufficient for us, and He is the Best Disposer of affairs.''
Al-Bukhari recorded that Ibn Abbas said,
حسبنا الله ونعم الوكيل
"("Allah Alone is Sufficient for us and He is the Best Disposer of affairs for us),''
"Ibrahim said it when he was thrown in fire.
Muhammad said it when the people said, `Verily, the people have gathered against you, therefore, fear them.' But it only increased them in faith, and they said, `Allah is Sufficient for us and He is the Best Disposer of affairs for us.'''
Abu Bakr Ibn Marduwyah recorded that Anas bin Malik said that the Prophet was told on the day of Uhud,
"Verily, the people have gathered against you, therefore, fear them.''
Thereafter, Allah sent down this Ayah (3:173)
This is why Allah said,