Is the position of tawarruk in the final tashahhud for every prayer, or only for the four-rak'ah prayer?

The tawarruk (left-side sitting) in prayer is a confirmed Sunnah of the Prophet, peace and blessings be upon him, and it has two forms: either one lays down the left foot and keeps the right foot upright, extending both out from the right side, and rests the buttocks on the ground; or one lays down both feet, extending them out from the right side, and rests the buttocks on the ground. Scholars have differed regarding its place [in prayer], and the preponderant opinion is that it occurs in the last tashahhud (testimony of faith) of a prayer that has two tashahhuds. However, if the prayer has only one tashahhud, then iftirash (spreading the left foot and sitting on it) is observed.