بِسْمِ اللهِ، وَعَلَى سُنَّةِ رَسُولِ اللهِ

In the name of Allāh and upon the Sunnah of the Messenger of Allāh.

Reference: In the name of Allāh and upon the Sunnah of the Messenger of Allāh. Abū Dāwud (#3213, 3/314) with a ṣaḥīḥ chain and Aḥmad (2/40) with the phrase: (<div lang="ar">بسم الله و على ملة رسول الله</div>) and its chain is ṣaḥīḥ.