Being Firm...

Shahr bin Haushab reported: I asked Umm Salamah (radhiAllahu anha), "O Mother of the Believers! Which supplication did the Messenger of Allah (sall'Allahu alayhi wasalam) make frequently when he was in your house?'' She said: "He (sall'Allahu alayhi wasalam) supplicated frequently: ` Ya muqallibal-qulubi, thabbit qalbi `ala dinika

(O Controller of the hearts make my heart steadfast in Your religion) .''
[At-Tirmidhi].

In addition, I found this nice explanation:

Supplicating,asking Allah to make us firm on His deen, is because He is the one who guides us to His deen and He alone makes us firm on it. There are so many people whom Allah did not guide them to the truth, and many people whom Allah guided to the truth but did not make them firm on that guidance. Because of a trial (test), they failed. About this kind of people, Allah says in surah Al-Hajj, (Verse 11), what can be translated as, "And among mankind is he who worships Allah as it were, upon the very edge (i.e. shaky in doubt); if good befalls him, he is content therewith; but if a trial befalls him, he turns back on his face (i.e. reverts back to disbelief after embracing Islam). He loses both this world and the Hereafter. That is the evident loss."

In the hadith related by Imams Muslim and Ahmad, the Prophet Muhammad (salallahu alayhi wa salam) said, "The hearts of the children of Adam are all between two fingers of the Compassionate’s fingers like one heart, He directs it in any direction he wills."

In an authentic hadith, it was reported by Imam At-Timithi that the Prophet (salallahu alayhi wa salam) used to say frequently this supplication, "O Allah, The One who changes hearts, make my heart firm on your deen. ". 

Inshallah, we should frequently say this supplication, and also say, "O our Lord, do not make our hearts go astray after you had guided us." And , "O our Lord, bless us with patience and help make our feet firm."

May Allah keep us firm upon Quran and Sunnah. ameen!

Asalaam alaykum wa rahmatullahi Wa Barakatuhu.