Reference: Liqaa. al-Baab al-Maftooh, Volume 25, Page 22
Question: Noble Shaykh, I notice some people, whilst in the sujood [position] they lift one of their feet, or [even] both. So what is the ruling regarding this action?
Response: It is not permissible for the one in sujood to lift any of the [required] seven [body] parts [from the ground], because the Prophet (sal-Allaahu ‘alayhi wa sallam) said:
«I have been commanded to make sujood upon seven parts (of the body): upon the length of the nose to the forehead, and he pointed with his hand to his nose, upon the palms of the hand, upon the knees and upon the tips of the toes»
So if anyone lifts one foot or both of them, or [lifts] his hand or both of them, or [lifts] his nose or his forehead of both of them, then certainly his sujood is nullified and not counted, and if his sujood is nullified, then indeed his [entire] salaah is nullified.