بسم الله الرحمن الرحيم
Q: What is the ruling on performing salat-ut-tasbeeh?
A: It is not authentically attributed to the Prophet -sallahu alayhi wa salaam- as he said, “whoever does an action that does not coincide with our command is rejected.” As long as it is not a firmly established practice it is impermissible to act in accordance with it. Furthermore contain therein are peculiarities from the perspective of how its performed, as the Prophet -sallahu alayhi wa salaam- prohibited recitation of the Quran while bowing and prostrating (during prayer) and in the aforementioned prayer there is recitation of the Quran in both places. Likewise there are aspects of it that contradict legislated prayers therefore indicating the lack of a foundation (in the religion) for this prayer, so pray -my brother- duha (the forenoon prayer), pray the night prayer, witr, the voluntaries prayers attached to the (5) obligatory prayers along with them, as the opportunities are available.
Translated by Najeeb Al Anjelesi
Source: شرح الأصول الستَّة