Firstly: The Ruling of Sitting Between the Two Prostrations
Sitting between the two prostrations is an integral of prayer. This is the position of the majority: the Maliki, Shafi`i, and Hanbali schools and one position among Hanafis.
Secondly: Asking for Forgiveness When Sitting Between the Two Prostrations
It is sunnah to ask for forgiveness between the two prostrations. This is the position of the Maliki and Shafi`i schools and some of the late Hanafis. It is also one narration from Ahmad and the position of the majority of scholars.
Thirdly: Where to Place the Hands When Sitting Between the Two Prostrations
One places the forearms against the thighs. The hands are placed on their corresponding thighs close to, or on, the knees. Consensus on this was related by Ibn `Abd al-Barr, al-Nawawi, and Ibn Juzayy.
It is sunnah to sit between the two prostrations in iftirash (with the buttocks resting on the left foot and the right foot erect, toes facing the qiblah). This is the position of the majority: the Hanafi, Shafi`i, and Hanbali schools.
It is sunnah to occasionally sit between the two prostrations in iq`a’.  Iq`a’ according in the sunnah manner is to place the tips of the toes on the ground and to sit on the ankles while the knees are on the ground. This is statement of al-Shafi`i, one narration from Ahmad, and the position of some of the Salaf. It is the chosen opinion of al-Bayhaqi, al-Qadi `Iyad, Abu `Amr ibn al-Salah, al-Nawawi, al-Kamal ibn al-Humam, al-Shawkani, Ibn Baz, and al-Albani.
Sixthly: Sitting Before Rising from Prostration
Scholars are of two positions regarding sitting after the second prostration and before rising for the second and fourth units of prayer:
The first position: It is not sunnah to sit before rising if one doesn’t need to. This is the position of the majority: the Hanafis, Malikis, and Hanbalis. It is one position in the Shafi`i school. Ibn al-Qayyim considered it the strongest position in terms of evidence, and Ibn `Uthaymin selected it.
The second position: Sitting before rising is sunnah. One does not stand for the second or fourth units of prayer until one first sits still. This is the position of the Shafi`i school, one narration from Ahmad and a group of Hadith specialists, and the position of Dawud al-Zahiri. Al-Shawkani, Ibn Baz, and al-Albani chose this position.