Dua After Salah

Thawban, Allah be pleased with him narrates that when the Messenger of Allah would complete his Salah he would seek Allah’s forgiveness three times and say:

O Allah, You are free from all defects and the grantor of security, Blessed are You, O owner of greatness and majesty.
It was asked from Al-Awzai (one of the narrators of the Hadith), How is Allah’s forgiveness to be sought (with which words). He replied that the individual should say ‘Astaghfirullah,Astaghfirullah’.