Ameerul Momineen (a.s.) narrates – Once I requested the Prophet (s.a.w.a.) to seek forgiveness for me.
He (s.a.w.a.) said – I will do it.
Then he (s.a.w.a.) rose, prayed namaz, then when he (s.a.w.a.) raised his hands in supplication, I heard him (s.a.w.a.) while he (s.a.w.a.) was reciting –
اللهم بحق علي عندك اغفر لعلي
‘O Allah by the right of Ali near you, forgive Ali.’
Then I said – O Prophet of Allah (s.a.w.a.), what is this?
He (s.a.w.a.) said – Had there been anyone nobler than you near Allah, I would have sought intercession through him near Allah.
Sharhe Nahj al-Balaaghah v 20 p 316 Mafaateh al-Jenaan Section of Baaqiyaat al-Saalehaat