Tafsīr al-ʿAyyāshi: From Ṣafwān al-Jamāl, who said:

Abū ʿAbd Allāh عليه السلام who said: Allāh did not send down a book from the heavens except that it’s opening was In the name of Allāh, The Entirely Merciful, The Especially Merciful (Bismillah al-Raḥmān al-Raḥīm). The cessation of one chapter is only known by the descension of In the name of Allāh, The Entirely Merciful, The Especially Merciful (Bismillah al-Raḥmān al-Raḥīm) as the beginning of another.

عن صفوان الجمال ، قال : قال أبو عبدالله ( عليه السلام ) : ما أنزل الله من السماء كتابا إلا وفاتحته * ( بِسْمِ اللَّه الرَّحْمنِ الرَّحِيمِ ) * وإنما كان يعرف انقضاء السورة بنزول * ( بِسْمِ اللَّه الرَّحْمنِ الرَّحِيمِ ) * ابتداء للأخرى