Silsilat al-Ahadith al-Sahihah

It is narrated from Sayyiduna Qais bin Sa'd bin 'Ubadah (may Allah be pleased with him) that my father left me with the Prophet Muhammad (peace and blessings be upon him) to serve him. (One day) the Prophet (peace and blessings be upon him) passed by me and I had already performed the prayer. The Prophet (peace and blessings be upon him) struck me with his foot and said: "Shall I not guide you to one of the gates of Paradise? (And that is this remembrance) «لاحول ولا قوة الا بالله» (There is no power to avoid evil and no strength to do good except through Allah's help)."