أَنتَ وَلِيُّنَا فَٱغۡفِرۡ لَنَا وَٱرۡحَمۡنَاۖ وَأَنتَ خَيۡرُ ٱلۡغَٰفِرِينَ.
You are our Protector, so forgive us and have mercy upon us; and You are the best of forgivers.
Anta Walliyyuna faghfir lana warhamna wa Anta khayrulghafirin.
Prophet Musa starts this supplication by appealing to Allah and referring to Him as their (i.e. he and the Children of Israel’s) Protecting Guardian. Such an appeal is appropriate before asking for Allah’s forgiveness and mercy. It is also a means by which Prophet Musa reaffirms their sincerity and their resolve to worship no one but Allah as an apology after the Children of Israel had taken the cow for worship. -Ibn ‘Ashoor.