Concept:The year 621 C.E. is linked to the Isra and Mi'raj, during which the obligatory daily prayers were given to Muslims.
Explanation:In 621 C.E., Prophet Muhammad undertook the Night Journey from Makkah to Jerusalem and ascended to the heavens.
During this journey, Allah made the five daily prayers, known as Salat, obligatory for Muslims.
This event gave Salat its place as the formal mode of worshipping Allah.
Therefore, 621 C.E. is remembered for the institution of Salat, not for Zakat, the return from Abyssinia, or the acceptance of Islam by Abu Talib.
Answer:D. Salat became a mode of worshipping Allah.