Shaikh Salih al Fawzan hafidhuhallah said:
“This person asks about making tarteel in dua. Tarteel is in the recitation of the Qur’aan The Qur’aan is read in tarteel. As for the speech of people, Dua and otherwise, it is not read in tarteel. That is madd (elongation), ghunna, and the rules of Tajweed are for the Qur’aan alone. As for the speech of the people, then no”.
[Taken from: https://m.youtube.com/watch?v=LfRAvwxRhO4&feature=youtu.be ]
Faisal ibn Abdul Qaadir ibn Hassan