Does the saying, "Astaghfirullah wa atubu ilayh (I seek forgiveness from Allah and repent to Him)" have a basis in the Sunnah, and is it obligatory to limit oneself solely to the Prophetic forms of seeking forgiveness?

The wordings of istighfar (seeking forgiveness) and tawbah (repentance) mentioned are correct and have been narrated in the Sunnah, such as: "Astaghfirullah wa atubu ilayh" (I seek forgiveness from Allah and repent to Him) and "Subhan Allah wa bihamdih, astaghfirullah wa atubu ilayh" (Glorified be Allah and praised be He, I seek forgiveness from Allah and repent to Him). It is not obligatory to be restricted to these specific wordings, as istighfar and tawbah can be performed with any wording that signifies them. However, the wordings mentioned in revelation are superior, among them is the statement of Allah Almighty: (Our Lord, so forgive us our sins and remove from us our misdeeds) and the saying of the Prophet (peace be upon him): "My Lord, forgive me and accept my repentance, for indeed You are the Acceptor of Repentance, the Most Merciful." The matter regarding the wordings of istighfar and tawbah is broad.