Does the prayer of one who intentionally omits the Taslim become void according to the Hanafis, taking into consideration Ibn Mas'ud's Hadith: "If you say this, or complete this - meaning the Tashahhud - then you have completed your prayer; if you wish to stand, then stand, and if you wish to sit, then sit"?

According to the Hanafis, the taslim (definition) (salutation) is among the wajibats (obligatory acts) of prayer, not a rukn (pillar). It appears from their statements that intentionally omitting it does not invalidate the prayer, but its re-performance becomes obligatory as a stricture upon the one who omitted it intentionally. Their evidence for it not being a pillar is the hadith (definition) of Ibn Mas'ud: "When you say this, or complete this, you have completed your prayer. If you wish to stand, then stand, and if you wish to sit, then sit." However, this hadith is weak and anomalous, and the correct view is that it is a statement of Ibn Mas'ud, and the Huffaz (Hadith masters) have agreed on the interpolation of this addition into it. Al-Bayhaqi narrated what contradicts this addition with the wording: "The key to prayer is the takbir, and its conclusion is the taslim when the Imam makes the taslim. If you wish, then stand." This narration from Ibn Mas'ud is authentic.