We were with the Messenger of Allah (Sallallaahu 'alaihi wasallam) when he asked, "Is anyone of you unable to earn a thousand good deeds?''
One of those present asked: "How can one earn thousand good deeds in a day?''
He (Sallallaahu 'alaihi wasallam) replied, "By saying: "Subhan Allah" a 100 times, then 1000 good deeds will be recorded for him or one thousand sins will be blotted out from his record.''
[Muslim]