Is sitting in the Tashahhud and between the two prostrations, relying on the knees without placing the buttocks, counted?

If a worshiper sits between the two prostrations or during the Tashahhud on his knees and the tips of his feet, placing his buttocks on his heels, then his sitting is sufficient and his prayer is valid. Although this sitting posture is contrary to the Sunnah, it does not invalidate the prayer.