🕯.. 290 – He narrated to us, he said: I asked my father about: a man doing tashahhud and breaking wudū before doing salām (in prayer)?
He said: he repeats the prayer; because he is in prayer as long as he doesn’t do salām, he went according to the hadīth of ‘Alī from the Prophet ﷺ: “Its dissolution is the tasleem”. (i.e. the salām at the end of the prayer is the dissolution of the prayer)
[Masāil Ahmad 📚, by his son Abdullah, pg 74]