Allah's Messenger (ﷺ) said:
"O Abdullah bin Qais, should I not point you to one of the treasures of Paradise?"
I said, "Yes, O Messenger of Allah."
So he told me to say:
Lā ḥawla wa lā quwwata 'illā billāh.
Allah's Messenger (ﷺ) said: "O Abdullah bin Qais, should I not point you to one of the treasures of Paradise?"
I said, "Yes, O Messenger of Allah."
So he told me to say:
There is no power and no might except by Allah.
Reference:
Al-Bukhari, cf. Al-Asqalani, Fathul-Bari 11/213, Muslim 4/2076.