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.
Sitting for a duration in which the last Tashahhud can be recited is one of the pillars of the prayer, according to the Hanafi School.
The Hanafi Fiqh book Minhat-us-Sulook fi Sharh Tuhfat-ul-Mulook reads about the pillars of the prayer:
“The sixth: the last sitting for the duration of Tashahhud. The duration of Tashahhud means the amount of time it takes to recite the Tashahhud until saying, ‘Abduhu wa rasooluhu’, because this is what is generally meant by Tashahhud when it is mentioned. It was also said, ‘The obligatory duration of the sitting is the time it takes to say the Shahaadatayn (the Two Testimonies of Faith).’ The first view is more correct. Proof that the last sitting is Fardh (obligation) is the statement of the Prophet who said, ‘If you raise your head from the last sitting position and you sit for the duration of Tashahhud, then your prayer is complete.’”
As regards reciting the first Tashahhud, or the last one, then these are among the Waajibaat (pl. of Waajib; it means obligations) of the prayer, according to the Hanafi School.
Ibn Nujaym, when talking about the Waajibaat of the prayer, said in Al-Bahr Ar-Raa’iq:
"His words, ‘and the Tashahhud,’ mean the first Tashahhud and the second Tashahhud; and in some versions of the book An-Niqaayah, it reads, ‘the Two Tashahhuds’. The Prophet continually observed them, and this is evidence that it is obligatory, as he said to Ibn Mas‘ood, ‘Say, 'At-Tahiyyaat…'’ without making a distinction between the first Tashahhud and the second one. A group of scholars had chosen the view that the Tashahhud in the first sitting position is a Sunnah to distinguish between the two sitting positions, because since the last sitting is a Fardh, then its Tashahhud is a Waajib, and since the first Tashahhud is a Waajib, then its Tashahhud is a Sunnah.”
The Hanafi School stated that if one abandons one of the Waajibaat of the prayer deliberately, his prayer is not invalidated but he must repeat it, and if he does not repeat it, he is considered a sinner and an impious person.
Ad-Durr Al-Mukhtaar, authored by Al-Haskafi from the Hanafi School, reads about the Waajibaat of the prayer, “There are some Waajibaat that do not invalidate the prayer if one leaves them, but the prayer must be repeated if one leaves them deliberately or did not prostrate for forgetfulness (Sujood as-Sahw), and if he does not repeat it, he is considered an impious sinner.”
Ibn ‘Aabideen said in his commentary on Ad-Durr Al-Mukhtaar, “His saying, ‘it must be repeated,’ i.e. because of leaving these Waajibaat or by leaving one of them.”
Based on the above, sitting in the Tashahhud without reciting it does not benefit you in dealing with the Waswasah according to the Hanafi School because of the obligation to repeat the prayer for not reciting the Tashahhud intentionally, as we have already discussed above. In addition, it is a pillar of the prayer, according to the Hanbali School; and according to the Shaafi'i School, the prayer is invalidated by leaving it.
The Kuwaiti Fiqh Encyclopedia reads, “The last Tashahhud: It is a pillar of the prayer according to the Shaafi'i and Hanbali Schools of Fiqh, as the Prophet said, ‘If one of you sits in prayer, let him say, 'At-Tahiyyaatu lillah…'’”
Therefore, we advise you to avoid Waswasah and not pay any attention to it and to recite the Tashahhud in a clear manner. The matter is easier than you imagine. Your fear of committing a mistake here is nothing but obsessive whispers, so you must avoid them and not pay any attention to them and seek refuge in Allah from the accursed devil.
You should supplicate Allah as much as possible and seek His Help, as He is near and He answers the supplications.
Allah knows best.