Remembering Allah by saying “Subhaan al-Malik al-Quddoos (Glory be to the Sovereign, the Most Holy)” following Witr prayer and not between the rak‘ahs of Taraweeh
Question

Is it prescribed to say “Subhaan al-Malik al-Quddoos (Glory be to the Sovereign, the Most Holy)” after praying four or eight rak‘ahs of Taraweeh? Shouldn’t that be said after finishing Witr prayer? Is it permissible to recite that dhikr in the mosque if we intend to complete the prayer with Witr at home? Should we recite prayers for forgiveness after praying each two rak‘ahs of Taraweeh?
Praise be to Allah.What is proven from the Prophet (blessings and peace of Allah be upon him) is that he used to say “Subhaan al-Malik al-Quddoos (Glory be to the Sovereign, the Most Holy)” following Witr prayer. So it is Sunnah for the worshippers to follow his example in that, whether you pray in the mosque or at home, and whether you pray separately or in congregation. But it is not prescribed to constantly recite this dhikr between the rak‘ahs of qiyaam al-layl (voluntary night prayers) or between the rak‘ahs of Taraweeh, because there is no report from the Prophet (blessings and peace of Allah be upon him), or from his Companions (may Allah be pleased with them) to suggest that they recited it between the rak‘ahs Taraweeh. What the Muslim must do is adhere to the Sunnah with regard to doing actions or refraining from them, and he should avoid adding anything to or taking anything away from the Sunnah. 
It was narrated from ‘Abd ar-Rahmaan ibn Abza (may Allah be pleased with him) that the Prophet (blessings and peace of Allah be upon him) used to recite in Witr “Sabbih isma Rabbika al-A’la (Glorify the name of your Lord, the Most High)…” [i.e., Soorat al-A’laa 87] and Qul yaa ayyuha’l-kaafiroon (Say (O Muhammad), ‘O al-Kaafiroon (disbelievers))…’” [i.e., Soorat al-Kaafiroon 109] and “Qul Huwa Allaahu ahad (Say (O Muhammad), ‘He is Allaah, (the) One)…” [i.e., Soorat al-Ikhlaas 112]. And after he said the tasleem he would say “Subhaan al-Malik al-Quddoos, Subhaan al-Malik al-Quddoos (Glory be to the Sovereign, the Most Holy)”, three times, raising his voice the third time.
Narrated by Abu Dawood at-Tayaalisi in al-Musnad (1/441); Ibn al-Ja‘d in al-Musnad (1/86); Ibn Abi Shaybah in al-Musannaf (2/93); Imam Ahmad in al-Musnad (24/72), and others, with many isnaads. It was classed as saheeh by more than one of the hadith scholars, such as Ibn Mulaqqin, al-Albaani, Shaykh Muqbil al-Waadi ‘iand the commentators on the ar-Risaalah edition of Musnad Ahmad, and others. 
The hadith scholars included it under chapter headings which indicate that it is mustahabb to recite this dhikr following Witr. Ibn Abi Shaybah narrated it under a chapter heading: What du‘aa’ a man should recite at the end of his Witr. Abu Dawood (may Allah have mercy on him) said: Chapter on Du‘aa’ after Witr. An-Nasaa’i (may Allah have mercy on him) said: Chapter on Tasbeeh after finishing Witr. Ibn Hibbaan included it under a chapter heading in his Saheeh (6/202): Mention of what it is mustahabb to say in glorification of Allah, may He be glorified and exalted, when he finishes his Witr. 
Imam an-Nawawi (may Allah have mercy on him) said:
 It is mustahabb to say three times after Witr: “Subhaan al-Malik al-Quddoos (Glory be to the Sovereign, the Most Holy)”.
End quote from al-Majmoo‘ Sharh al-Muhadhdhab (4/16). See also: Tuhfat al-Muhtaaj (2/227) 
Ibn Qudaamah (may Allah have mercy on him) said: 
It is mustahabb to say after Witr: “Subhaan al-Malik al-Quddoos (Glory be to the Sovereign, the Most Holy)” three times, and to elongate the vowel the third time.
End quote from al-Mughni (2/122) 
Something similar was said in Fataawa al-Lajnah ad-Daa’imah (vol. 2, 6/60): When he says salaam at the end of Witr, he should say “Subhaan al-Malik al-Quddoos (Glory be to the Sovereign, the Most Holy)” three times. End quote. 
By the same token, we have not come across any of the scholars saying that it is mustahabb to recite the words “Subhaan al-Malik al-Quddoos (Glory be to the Sovereign, the Most Holy)” in any prayer other than Witr. 
On our website we have already explained that it is disallowed to recite adhkaar in unison, as is customary in some mosques, between the rak‘ahs of Taraweeh, whether that is istighfaar (prayer for forgiveness) or tasbeeh. Gathering to recite dhikr without any shar‘i evidence brings a person closer to bid‘ah (innovation) and further away from the Sunnah. 
Conclusion: it is not prescribed for the worshippers to say “Subhaan al-Malik al-Quddoos (Glory be to the Sovereign, the Most Holy)” between the rak‘ahs or Taraweeh; rather that should be after Witr. It is not prescribed to recite prayers for forgiveness in unison between the rak‘ahs of Taraweeh, but reciting prayers for forgiveness and tasbeeh individually is permissible.
For more information, please see: 37753, 50718, 108506, 121270 and 190881
And Allah knows best.