وَعَدَ اللَّهُ الَّذِينَ آمَنُوا مِنْكُمْ
Allah promised those who believed from among you.
The four caliphs—Abū Bakr, ʿUmar, ʿUthmān and ʿAlī—were present and had embraced Islam when the verse was revealed. Their caliphate is linked with this promise of succession.
Their period of leadership is designated by the particular term the Rightly Guided Caliphate.