بيعة
Bayʿah
The nomination of the Khalifah by the leaders of the Ummah, or its endorsement by the community; also the pledge given to the Prophet (peace be upon him) at Madinah.
What it means
Bayʿah is a pledge of allegiance, from a root meaning to give a hand in agreement. Faruqi lists two senses. In the first it is the nomination of the khalīfa by the leaders of the ummah, or the endorsement of that choice by the community at large. In the second it is the covenant that the first Muslims of Madinah made with the Prophet Muhammad (peace be upon him), promising obedience, allegiance and protection.
The Quran says that those who pledge allegiance to the Prophet are pledging it to God (48:10), and that God was pleased with the believers who pledged under the tree (48:18). After the Prophet’s death the practice was used for the succession of the caliphs, and it remains the model for a ruler’s acceptance by the community. The oath is a mutual agreement between ruler and ruled.
Often misunderstood as
That it is a feudal oath of submission, when it is a mutual covenant that binds both the ruler and the community.
What the sources say
The pledge under the tree was taken at Hudaybiyya, and Muslim writers on government have treated bayʿa as the legal basis of the caliphate.
Term and Arabic as listed in Ismail al Faruqi, Toward Islamic English (International Institute of Islamic Thought, 1995), p. 25, listed as BAY'AH. The definition is restated here.