To what extent is it legislated to deliver religious lessons after the first four rak'ahs of Tarawih prayer, and what is the evidence for the bid'ah (innovation) of denying the remembrance of Allah and the recitation of short surahs or sending blessings upon the Prophet after every two rak'ahs of Tarawih?

The Fatwa's Summary: There is no reported practice from the Companions specifying a particular dhikr (remembrance of God) or du'a (supplication) between the rak'ahs of Tarawih prayers. Ibn al-Hajj al-Maliki even considered the dhikr and raising one's voice with it after every two salutations of the Tarawih prayer to be an innovation (bid'ah). What is legislated for the worshippers during these breaks is for each person to engage in dhikr, recitation of the Qur'an, or to remain silent and rest. Some scholars have permitted this admonition between the rak'ahs for the benefit of educating people and reducing commotion, but it should be omitted at times lest people believe it to be part of the Sunnah.

Shaykh Al-Uthaymeen mentioned that there is no harm in reminding worshippers to straighten their rows. As for admonition, it should not be a regular habit. If it is intended as an act of worship, it becomes an innovation. Rather, it should only occur when there is a need for it, especially with the prevalence of ignorance and the increase in evil deeds.