The verse you are referring to is from Surah An Nisa (Verse # 48 to be exact)

"Indeed, Allah does not forgive association with Him, but He forgives what is less than that for whom He wills. And he who associates others with Allah has certainly fabricated a tremendous sin"
Urdu
خدا اس گناہ کو نہیں بخشے گا کہ کسی کو اس کا شریک بنایا جائے اور اس کے سوا اور گناہ جس کو چاہے معاف کردے اور جس نے خدا کا شریک مقرر کیا اس نے بڑا بہتان باندھا
(4:48)
Moreover, To Him belong the Most Beautiful Names. (20:8)
HE is At-Tawwib _The Guide to Repentance. Al-Afu_The Forgiver. Al-Ghaffar_The Forgiving.Al-Halim_The Forebearing.Al-Karim_The Generous. Al-Mujib_The Responder to prayer . Ar-Ra’uf_The Clement.Ar Rahim_The merciful
So provided the repentance is genuine, surely the odds are in the favour of its acceptance

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