Is Tawarruk obligatory or Sunnah?

Q 10: Is Tawarruk (placing the left foot under the right leg and sitting on the posterior during the last Tashahhud) Wajib (obligatory) or Sunnah (supererogatory act of worship following the example of the Prophet) in all Salahs (Prayers) or only those with more than two Rak`ahs (units of Prayer)?

A: There is textual evidence regarding the manner of sitting in the first Tashahhud (testification recited in the sitting position in the second unit of Prayer), between the two Sajdahs (prostrations) and in Tawarruk. This includes the Hadith reported on the authority of Wa'il Ibn Hujr that he watched the Prophet (peace be upon him) while he was offering Salah; he performed Sujud, then he sat and stretched out his left foot (to sit on it). Narrated by Ahmad, Abu Dawud and Al-Nasa'y. In another narration by Sa`id ibn Mansur, he said, I offered Salah behind the Prophet (peace be upon him). When he sat down to say Tashahhud, he stretched the left foot on the ground sitting on it. It was also reported on the authority of Rifa`ah ibn Rafi` that the Prophet (peace be upon him) said to a Bedouin, When you perform Sujud, be firm in your prostration; and when you sit, stretch your left foot on the ground and sit on it. Narrated by Ahmad. It was mentioned in the Hadith reported on the authority of Abu Humayd that When he sat between the two Rak`ahs, he used to sit on his left foot and spread the right one. In the last Rak`ah, he used to precede his left foot, spread the right one and sit on his buttocks. Narrated by Al-Bukhari. Thus, it becomes clear that Tawarruk is a Sunnah in the last Tashahhud (testification recited in the sitting position in the last unit of Prayer) in three-and four-Rak`ahs-Salah, according to the mentioned Hadith of Abu Humayd. And Allah knows best.May Allah grant us success. May peace and blessings be upon our Prophet Muhammad, his family, and Companions.