Silsilat al-Ahadith al-Sahihah

Shahr bin Hawshab says that I asked Sayyida Umm Salamah (may Allah be pleased with her): O Mother of the Believers! When the Messenger of Allah (peace and blessings be upon him) was with you, which supplication did he recite most frequently? She said: He (peace and blessings be upon him) used to recite this supplication most often: "O Turner of the hearts! Keep my heart firm upon Your religion." When he (peace and blessings be upon him) was asked about the reason for this supplication, he said: "The heart of every person is between two fingers from among the fingers of Allah, He keeps firm whomever He wills (upon guidance) and lets go astray whomever He wills."