رَبَّنَا لَا تُزِغْ قُلُوبَنَا بَعْدَ إِذْ هَدَيْتَنَا

Our Lord! Let not our hearts deviate (from the truth) after You have guided us.

meaning, "Do not deviate our hearts from the guidance after You allowed them to acquire it. Do not make us like those who have wickedness in their hearts, those who follow the <b>Mutashabih</b> in the Qur'an. Rather, make us remain firmly on Your straight path and true religion."
 
وَهَبْ لَنَا مِن لَّدُنكَ

And grant us from <b>Ladunka</b>,

meaning, from You,
 
رَحْمَةً

Mercy,

with which You make our hearts firm, and increase in our Faith and certainty,
 
إِنَّكَ أَنتَ الْوَهَّابُ
 
 

Truly, You are the Bestower. 

Ibn Abi Hatim and Ibn Jarir recorded that Umm Salamah said that the Prophet used to supplicate,

يَا مُقَلِّبَ الْقُلُوبِ ثَبِّتْ قَلْبِي عَلَى دِينِك

O You Who changes the hearts, make my heart firm on Your religion