Turning the Head Slightly During Prayer
25-3-2019 | IslamWeb
Question:
Assalum alaikum wa rahmatullahi wa barakatuhu. In the final rakaa of my prayer, after reciting salatul Ibrahimiyyah, I turned my face to my right side (as someone would do when saying the tasleem) and said the beginning of the dua after the tashahud (allahuma inni authu bika min athabi jahannam) without completing it. After I had realized my face was turned to the right as though I was saying the tasleem, I turned my head back so that it is facing towards the qibla and repeated the dua and completed it, then said the tasleem. Was it prescribed for me to perform Sujood as-Sahw in this case? If so, please clarify, barakallahu feekum, whether it was supposed to be performed before or after the tasleem, and if I should repeat the prayer or do wudu and perform sujood as-sahw, as there is an opinion that says that it is prescribed for the worshipper to perform sujood as-sahw even if it is after a long time? Jazakumullahu khairan
Answer:
All perfect praise be to Allah, The Lord of the Worlds. I testify that there is none worthy of worship except Allah, and that Muhammad 
is His slave and Messenger.
Your prayer is valid and it is not invalidated by turning your head to the right side, as long as you did not totally turn away from the Qiblah with your chest.
The jurists stated that "if the praying person turns in prayer without turning his chest, then this does not harm."
You are not required to prostrate for forgetfulness for this turning.
An-Nawawi 
said while listing what does not require the prostration for forgetfulness:
"Turning, making one step, or two steps according to the most correct view, one hit [like hitting a fly for example] or two hits, sitting in a squatting position, putting the hand on the mouth or on the hip, thinking during the prayer, looking at something that distracts, looking up to the sky, rolling up the garment or the hair, wiping the gravel, yawning, uselessly touching one’s beard or nose, and other similar movements; one is not required to prostrate for doing any of them, whether he did that (move) deliberately or out of forgetfulness." [End of quote]
Allah knows best.