I heard Messenger of Allah (PBUH) saying:
"When the time for a prescribed Salah is due and a Muslim performs its Wudu' and its acts of bowing and prostration properly, this Salah will be an expiation for his past sins, so long as he does not commit major sins, and this applies for ever.''
[Muslim]
Commentary:
This Hadith stresses the importance of performing Salat with all its essential prerequisites, i.e., Wudu' and concentration of mind. Such a Salat will expiate the sins.
Riyad-us-Saliheen – Hadeeth No. 1046