al-Tahdhīb: Moḥammed bin al-Ḥassan al-Ṭūsi, from Moḥammed bin ʿAlī bin Maḥbūb, from al-ʿAbbas, from Moḥammed bin Abī ʿUmayr, from Abī Ayūb, from Moḥammed bin Muslim1 who said:

I asked Abā ʿAbd Allāh عليه السلام about the seven repeated verses2 and the Glorious Qur’ān3 – is the seven repeated verses al-Fātiḥa?
He said: “Yes.”
I then said: In the name of Allāh, The Entirely Merciful, The Especially Merciful (Bismillah al-Raḥmān al-Raḥīm), is that from among the seven verses?
He said: “Yes, and it is the best of them.”

1. The ḥadīth has an authentic (Ṣaḥiḥ) chain.
2. The seven repeated verses (al-Sabʿ al-Mathāni) is usually considered in reference to al-Fātiḥa. Al-Mathāni is more literally translated as twice. Scholars have stated that al-Fātiḥa is given this title because it is repeated twice in every obligatory prayers. The other opinion is that it was revealed twice, once in Mekka and once in Medina.
3. al-Fātiḥa and the Qur’ān are mentioned separately, to show the greatness and significance of al-Fātiḥa itself – as Allāh mentions in the Qur’ān, al-Ḥijr (15:87) لقد ءاتيناك سبعا من المثاني و القران العظيم (Indeed we have given you the seven often repeated verses and the Glorious Qur’ān).

التهذيب: محمد بن الحسن الطوسي ، بإسناده عن محمد بن علي بن محبوب ، عن العباس ، عن محمد بن أبي عمير ، عن أبي أيوب ، عن محمد بن مسلم ، قال: سألت أبا عبدالله (عليه السلام) عن السبع المثاني والقرآن العظيم ، أهي الفاتحة؟ .  قال: نعم.  قلت: ( بِسْمِ اللَّهِ الرَّحْمنِ الرَّحِيمِ) من السبع؟  قال: نعم  ، هي أفضلهن