Primary condolence
إِنَّ للَّهِ مَا أَخَذَ، وَلَهُ مَا أَعْطَى، وَكُلُّ شَيْءٍ عِنْدَهُ بِأَجَلٍ مُسَمَّى... فَلْتَصْبِرْ وَلْتَحْتَسِبْ
Inna li-llāhi mā akhadha, walahu mā aʿṭā, wakullu shayʾin ʿindahu bi-ajalin musammā... faltaṣbir waltaḥtasib
Indeed, to Allah belongs what He has taken, and to Him belongs what He has given. Everything with Him has an appointed term. So let her be patient and seek Allah’s reward.
The final two Arabic verbs address a woman. Adjust their forms for the person being addressed.
Alternative condolence
Or say:
أَعْظَمَ اللَّهُ أَجْرَكَ، وَأَحْسَنَ عَزَاءَكَ، وَغَفَرَ لِمَيِّتِكَ
Aʿẓama llāhu ajraka, wa aḥsana ʿazāʾaka, wa ghafara li-mayyitik
May Allah increase your reward, comfort you in your bereavement, and forgive your deceased.
This is also good.