Does the ablution become void by saying the taslim during prayer (before its completion)?

Ablution is not invalidated by intentionally saying "As-salamu alaykum" before finishing the prayer, but the prayer itself becomes invalid. One who doubts the number of Rak'ahs should base their prayer on the lesser number and not say "As-salamu alaykum." Similarly, one who doubts having omitted a prostration should perform it and whatever follows it, then say "As-salamu alaykum." This applies to those who are not afflicted by obsessive doubt; as for the one who is, their obsessive doubts are not to be heeded, and they should not repeat their prayer because of them.