The fuqaha’ are agreed that the prostration of recitation is prescribed, because of the verses and hadeeths that are narrated concerning that. When the Muslim comes to a verse in which there is a sajdah, it is prescribed for him to prostrate, whether that is in prayer or outside of prayer. Muslim narrated in his Saheeh (81) that Abu Hurayrah (may Allah be pleased with him) said: “When the son of Adam recites a verse of prostration and prostrates, the Shaytaan withdraws, weeping and saying: Woe unto him – according to the report of Abu Kurayb: Woe unto me – the son of Adam was commanded to prostrate and he prostrated, so Paradise will be his; I was commanded to prostrate and I refused, so Hell is mine.”
So it is essential for him to prostrate and it is not valid to recite tasbeeh or any other dhikr instead of that; rather this is an innovation which should be denounced.
It was narrated that ‘Aa’ishah (may Allah be pleased with her) said: The Messenger of Allah (blessings and peace of Allah be upon him) said: “Whoever introduces into this matter of ours anything that is not part of it will have it rejected.” Agreed upon.
This hadeeth represents an important principle of Islam, and it is an example of the concise speech of the Prophet (blessings and peace of Allah be upon him), for it clearly rejects every innovation and fabrication. End quote.
And the Prophet (blessings and peace of Allah be upon him) said: “you must adhere to my Sunnah and the way of the Rightly Guided Caliphs. Hold on to it and cling fast to it. And beware of newly-invented matters, for every newly-invented matter is an innovation and every innovation is a going astray.” Narrated by Abu Dawood (4607) and classed as saheeh by al-Albaani in Saheeh Abi Dawood.
Ibn Hajar al-Haytami (may Allah have mercy on him) was asked about some of them saying, “We hear and obey, Your forgiveness Our Lord, and to You is our destiny” when not doing the prostration for a verse of prostration because one is not in a state of purity or is unable to prostrate.
He replied: There is no basis for that and it cannot take the place of the prostration; rather that is makrooh to do that, because nothing concerning that was narrated. End quote.
Al-Fataawa al-Fiqhiyyah al-Kubra, 1/194
Shaykh Ibn ‘Uthaymeen (may Allah have mercy on him) was asked: When we read the Book of Allah and we come to a sajdah, and we are in a place other than the mosque or prayer room, such as the school and the like, we say Laa ilaaha ill-Allaah wahdahu laa shareeka lah, lahu’l-mulk wa lahu’l-hamd wa huwa ‘ala kulli shay’in qadeer (there is no god but Allaah alone, with no partner or associate. His is the Dominion and to Him be praise, and He is able to do all things) four times. Is that permissible or not? If it is not permissible, what should we do?
When the reader comes to a verse of prostration, if he is in a place where he can prostrate, then it is mustahabb for him to prostrate, but it is not obligatory according to the more correct opinion, because it is proven that ‘Umar ibn al-Khattaab (may Allah be pleased with him) recited a verse of prostration when he was delivering the khutbah on a Friday, and he came down (from the minbar) and prostrated, then he recited it on the following Friday and did not prostrate, and he said: Allah has not enjoined us to prostrate unless we want to. And when he did not prostrate, he did not say something instead of prostrating, because that is an innovation. The evidence that is that Zayd ibn Thaabit recited Soorat al-Najm in the presence of the Prophet (blessings and peace of Allah be upon him) and he did not prostrate, and the Prophet (blessings and peace of Allah be upon him) did not teach him to say anything instead of prostrating. End quote.
Fataawa Islamiyyah, 4/66
And Allaah knows best.