Varying and combining the adhkaar to be recited when bowing
Question

                A number of adhkaar have been narrated to be recited when bowing, such as “Subhaan Allaah al-‘Azeem wa bi hamdihi (Glory and praise be to Allaah the most Great)” and “Subbooh Quddoos Rabb al-Malaa’ikah wa’l-Rooh (Glorified, Holy, Lord of the Angels and of the Rooh)” and “Allaahumma laka raka’tu … (O Allaah, to You have I bowed…)”. Is it permissible to combine two of these kinds of adhkaar when bowing, such as saying, “Subhaan Rabbiy al-‘Azeem (Glory be to my Lord Most Great” three times then saying, “Subbooh Quddoos Rabb al-Malaa’ikah wa’l-Rooh (Glorified, Holy, Lord of the Angels and of the Rooh)” three times?.
Praise be to Allah.
    Firstly: 

    The following reports have been narrated concerning the 
    adhkaar to be recited when bowing: 

    1 – Saying “Subhaana Rabbiy al-‘Azeem (Glory be to my 
    Lord Most Great)”, because of the report narrated by Muslim (772) from 
    Hudhayfah (may Allaah be pleased with him) who said: 

    I prayed with the Prophet  (peace and blessings of Allaah 
    be upon him) one night… then he bowed and he started saying: “Subhaana 
    Rabbiy al-‘Azeem (Glory be to my Lord Most Great).” 

    2 – Saying “Subhaana Rabbiy al-‘Azeem wa bi hamdihi 
    (Glory and praise be to my Lord Most Great)”, because of the report narrated 
    by Abu Dawood from ‘Uqbah ibn ‘Aamir (may Allaah be pleased with him) who 
    said: 

    When the Messenger of Allaah  (peace and blessings of 
    Allaah be upon him) bowed, he would say: “Subhaana Rabbiy al-‘Azeem wa bi 
    hamdihi (Glory and praise be to my Lord Most Great)” three times, and 
    when he prostrated he would say: “Subhaana Rabbiy al-A’laa wa bi hamdihi 
    (Glory and praise be to my Lord Most High)” three times.

    Classed as saheeh by al-Albaani in Sifat al-Salaah, p. 
    133. 

    3 – Saying “Subbooh Quddoos Rabb ul-Malaa’ikah wa’l-Rooh 
    (Glorified, Holy, Lord of the Angels and of the Rooh)” because of the report 
    narrated by Muslim (487) from ‘Aa’ishah (may Allaah be pleased with her), 
    according to which the Messenger of Allaah  (peace and blessings of 
    Allaah be upon him) used to say when bowing and prostrating: “Subbooh 
    Quddoos Rabb ul-Malaa’ikah wa’l-Rooh (Glorified, Holy, Lord of the 
    Angels and of the Rooh)”. 

    4 – Saying: “Subhaanaka Allaahumma Rabbana wa bihamdika, 
    Allaahumma ighfir li (Glory and praise be to You, O Allaah our Lord; O 
    Allaah, forgive me)” because of the report narrated by al-Bukhaari (794) and 
    Muslim (484) from ‘Aa’ishah (may Allaah be pleased with her) who said:

    The Prophet  (peace and blessings of Allaah be upon him) 
    used to say when bowing and prostrating: “Subhaanaka Allaahumma Rabbana 
    wa bihamdika, Allaahumma ighfir li (Glory and praise be to You, O Allaah 
    our Lord; O Allaah, forgive me)”. 

    5 – Saying, “Allaahumma laka raka’tu wa bika aamantu … 
    (O Allaah, to You have I bowed and in You have I believed…)” because of the 
    report narrated by Muslim (771) from ‘Ali ibn Abi Taalib (may Allaah be 
    pleased with him) , according to which when the Messenger of Allaah  
    (peace and blessings of Allaah be upon him) bowed, he would say: “Allaahumma 
    laka raka’tu wa bika aamantu wa laka aslamtu, khasha’a laka sam’i wa basari 
    wa mukhkhi wa ‘azmi wa ‘asabi (O Allaah, to You have I bowed and in You 
    have I believed and to You have I submitted; my hearing, my sight, my brain, 
    my bones and my sinews submit to You).” 

    Secondly: 

    The Muslim should preserve these Sunnahs that have been 
    narrated from the Messenger  (peace and blessings of Allaah be upon 
    him), so he should say one of them sometimes and another of them sometimes. 
    And he may combine all these adhkaar in one bowing. 

    Al-Nawawi (may Allaah have mercy on him) said in 
    al-Adhkaar (p. 86): But it is better to combine all of these adhkaar if 
    that is possible without causing hardship to anyone else, and he should 
    recite the tasbeehs first (those that start with the words Subhaan Allaah). 
    If he wants to keep it short then it is mustahabb to say tasbeeh, and the 
    minimum required is to say tasbeeh three times, but if he says it only once 
    he will have done what is basically required for tasbeeh. If he wants to 
    limit it to only some of the adhkaar, it is mustahabb to say some of them 
    sometimes and others at other times and so on, so that he will have done all 
    of them. End quote. 

    It says in al-Iqnaa’, which is a Hanbali book (1/119): 
    It is not makrooh to add something to the phrases “Rabb ighfir li 
    (Lord forgive me) or to say more than “Subhaana Rabbiy al-‘Azeem 
    (Glory be to my Lord Most Great)” and “Subhaana Rabbiy al-‘Ala (Glory 
    be to my Lord Most High)” when bowing and prostrating. End quote 

    Shaykh Ibn ‘Uthaymeen (may Allaah have mercy on him) said in al-Sharh al-Mumti’ (3/77), after mentioning a number of adhkaar to be said when bowing and raising the question as to whether these adhkaar may be combined or one should recite only one of them: 

    This is possible. We have stated above that not all of the opening du’aa’s that have been narrated should be said at once, rather we should say one of them sometimes and another at other times, and we have quoted the evidence for that. But with regard to the adhkaar for bowing which are known to most of the scholars, they may all be recited together. End quote.