Bukhari

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Narrated Aisha: When the Surat-An-Nasr", 'When comes the Help of Allah and the conquest,' had been revealed to the Prophet he did not offer any prayer except that he said therein, "Subhanka Rabbana wa bihamdika; Allahumma ighfirli (I testify the Uniqueness of our Lord, and all the praises are for Him: O Allah, forgive me!")

It has been said that by «لكم دينكم‏» is meant disbelief (kufr), and by «ولي دين‏» is meant Islam. «ديني» is not said because the verses end with the letter "noon" (ن). Therefore, here too, the "yaa" (ی) has been omitted, just as it is said «يهدين ويشفين‏.‏». Others have said that it means: "Now I will not worship your deities," that is, the deities you are worshipping at this time, "nor will I accept your religion for the rest of my life, nor will you worship my deity." By this are meant the disbelievers, about whom Allah the Exalted has said: «وليزيدن كثيرا منهم ما أنزل إليك من ربك طغيانا وكفرا‏» al-ayah, meaning: "And what is revealed to you from your Lord increases many of them in rebellion and disbelief."