A desert Arab came to Allah’s Messenger (saw) and said, “Teach me a word that I can say.”
The Prophet (saw) told him to say:
There is none worthy of worship but Allah, Who has no partner, Allah is the Great, the Most Great, and praise is to Allah in abundance, glory is to Allah. Lord of the worlds. There is no power and no might but by Allah the Mighty, the Wise.
He said, “That is for my Lord, but what about me?” The Prophet (saw) told him to say,
O Allah forgive me, have mercy on me, guide me and provide for me.
reported in Muslim 4/2072
Abu Dawud reports the same hadith with the addition:
“..and when the Arab left, the Prophet (saw) said, “He has filled his hands with goodness” 1/220
[translation taken from Fortress of the Muslim: Invocations from Qur’an & Sunnah published by Darussalam]