What is the ruling on supplicating with "O Allah, O Ever-Subtle, You have always been Subtle, be Subtle concerning what has descended" between the rak'ahs of Tarawih, and what is the ruling on reciting Surat "Qul Huwa Allah Ahad" and sending blessings upon the Prophet, peace and blessings be upon him, between the Tarawih prayers?

The first supplication is permissible because it is a request to Allah using His name, Al-Latif (The Subtle, The Gracious). The general rule for reciting Surah Al-Ikhlas and sending prayers upon the Prophet (peace be upon him) is that it is permissible. Remembrance (dhikr) is desired and legislated, as Allah Almighty says: "Remember Allah with much remembrance," and as the Prophet (peace be upon him) said: "Let your tongue remain moist with the remembrance of Allah." However, singling out a specific remembrance at a specific time, and with a loud voice in a group, requires evidence; otherwise, it is an innovation (bid'ah), based on the Prophet's (peace be upon him) saying: "Whoever introduces into this matter of ours that which is not from it will have it rejected." Sheikh Al-Islam Ibn Taymiyyah issued a fatwa that the Sunnah in supplication is to do it quietly, unless there is a reason that necessitates vocalization, and this is by scholarly consensus. Therefore, raising the voice with prayers upon the Prophet (peace be upon him) is disliked or forbidden.