Is it permissible for the Companions to innovate in religion, such as by establishing the Hijri calendar?

Establishing the Hijri calendar is not an innovation (bid'ah); rather, it falls under the category of al-masalih al-mursalah (unrestricted public interests), which are matters that did not exist during the Prophetic era and lack specific textual evidence. Al-Shatibi clarified that many confuse innovations with masalih mursalah.

Innovation differs from maslahah mursalah in several ways: 1. The Aspect of Worship: Innovation pertains to matters of worship, whereas maslahah mursalah pertains to matters with discernible meanings. 2. Intent: Innovation is intended for its own sake as an act of drawing closer to Allah, while maslahah mursalah has a secondary intent, serving as a means to achieve the objectives of Sharia. 3. Impact: Innovation leads to stringency and hardship, while maslahah mursalah aims to lighten the burden and remove hardship. 4. Conformity with Sharia Objectives: Innovation contradicts the objectives of Sharia, whereas maslahah mursalah serves them. 5. Reason for Not Occurring in the Prophetic Era: The non-occurrence of maslahah mursalah in the Prophetic era was due to the absence of a necessitating factor or the presence of an impediment. As for innovation, it did not occur despite the presence of a necessitating factor.

The consensus of the Companions and the actions of the Rightly Guided Caliphs cannot be considered an innovation; rather, they fall within the concept of Sunnah. This is indicated by the Prophet's (peace be upon him) saying: "Hold fast to my Sunnah and the Sunnah of the Rightly Guided Caliphs." The Companions agreed upon dating by the Prophet's migration (Hijrah).