Musnad Ahmad 1259:0

Narrated Umm Hakim bint al-Zubayr ibn Abd al-Muttalib: The Messenger of Allah (ﷺ) said: "Whoever performs ablution and performs it well, then prays two rak'ahs, not letting his soul wander in them, his sins will be forgiven, as they were on the day his mother gave birth to him." She said: I said to him: "O Messenger of Allah, even if I have committed major sins?" He said: "Even if you have committed major sins."