Shaykh Ibn Uthaymeen was asked the following question:
What is the ruling on the sermon/talk between the Salatul-Taraaweeh or in the middle of it and it (being) constantly (done)?
As for the sermon, then no because this is not from the guidance of the salaf, but he admonishes them if there is a need or if he wills after the taraaweeh. And if he intends by it worship, then this is an innovation. And the sign of intending worship is that he persists in doing it every night. Then we say, “Why, oh brother, do you give a sermon to the people?” Perhaps some people have work; they want to finish taraaweeh and leave to reach the statement of the Messenger (praise and peace be upon him): “Whoever stands with the imam until he finishes, it is written for him Qiyaamu Layl.” And if you love the sermon and also half of the people love it rather three fourths of the people love it, then do not imprison the last fourth because of what is loved by the three fourths. Did not the Messenger (praise and peace be upon him) say, “If one of you leads the people, then make it light. Verily from those who are behind him are the weak and sick and one with a need” or as he said (praise and peace be upon him). It means that you do not measure the people by yourself or by the others who love the speech and the sermon. Measure the people by that which eases them. Lead them in taraaweeh, and when you are finished with that and you have finished your salaat and the people have finished, then say what you will from speech.”
Ali ibn Nathaniel Grays
Source: Taken from an Arabic site but its origin is from ( لقاء الباب المفتوح 118)