It was narrated from Abu Hurairah that:
The Messenger of Allah (ﷺ) [SAW] was asked: "Which deed is best?" "He said: Faith in Allah [SWT] and His messenger [SAW]."
It was narrated from Abdullah bin Hubshi Al-Khath'ami that:
The Prophet (ﷺ) [SAW] was asked: "Which deed is best?" He said: "Faith in which there is no doubt, Jihad in which there is no Ghulul, and Hajjatun Mabrur."