Saying du’aa’ al-istikhaarah without praying
Question

                Is it permissible to recite the du’aa’ of istikhaarah without praying two rak’ah beforehand, because one is not at home, for example?.
Praise be to Allah.Istikhaarah means asking 
    Allaah to help you choose the better of two things and to divert the worse 
    of them. Praying two rak’ahs beforehand is only prescribed before the du’aa’ 
    to make it more likely to receive a response, and to help bring about proper 
    presence of mind and make the du’aa’ more likely to be accepted. 
Ibn Abi Jamrah said, as 
    narrated in Fath al-Baari (11/186): 
The wisdom behind putting 
    the prayer before the du’aa’ is that the aim of istikhaarah is combine the 
    best of this world and the Hereafter. So he needs an introduction before 
    presenting his case before Allaah, as it were. And there is nothing better 
    for that than prayer, because it involves venerating Allaah, praising Him 
    and expressing one’s need for Him now and always. End quote. 
The istikhaarah that the 
    Prophet  (peace and blessings of Allaah be upon him) taught us includes 
    praying two rak’ahs then reciting the du’aa’ after that. 
If a Muslim cannot offer 
    the prayer (two rak’ahs) for some reason, there is nothing wrong with 
    calling upon Allaah and asking Him to make easy for him the better of the 
    two options, without offering the prayer. 
Al-Nawawi (may Allaah have 
    mercy on him) said in al-Adhkaar (p. 120): 
If he cannot offer the 
    prayer then he may recite the du’aa’ of istikhaarah. End quote. 
These words of al-Nawawi 
    were quoted by a number of scholars from different madhhabs, who quoted them 
    as evidence. 
See: Haashiyat Radd 
    al-Muhtaar (2/27); al-Fawaakih al-Dawaani (1/35); Sharh 
    Mukhtasar Khaleel by al-Kharashi (1/37); Asna’l-Mataalib (1/205). 
And Allaah knows best.