During the tenure of which caliph was Tarawih prayed in congregation (Ba Jammat) for the first time?

The congregational prayer of Tarawih (Ba Jammat) was formally established and prayed for the first time during the caliphate of Hazrat Umar (RA). While the Prophet Muhammad (PBUH) and Hazrat Abu Bakr (RA) prayed Tarawih, it was often individually or in small groups. Hazrat Umar (RA) observed people praying in scattered groups and decided to unify them under one Imam, Ubayy ibn Ka'b, to ensure a more organized and consistent practice during Ramadan nights.

• Hazrat Abu Bakr (RA) was the first caliph, but the formal congregational practice was not during his time.
• Hazrat Usman (RA) and Hazrat Ali (RA) were later caliphs, by which time the practice was already established.

Thus, Hazrat Umar (RA) is credited with organizing the congregational Tarawih prayer.