Al-Dahhak reported: The Messenger of Allah, peace and blessings be upon him, said, “Allah Almighty says: I am the best partner. Whoever associates another partner with me, it is only done for the sake of my partner.” Then, the Prophet said, “O people, make your deeds sincere for Allah Almighty. Verily, Allah does not accept any deed unless it is sincerely for him. Do not say: This is for the sake of Allah, and this is for the sake of my relatives. Verily, it was done for your relatives and none of it was for Allah. Do not say: This is for the sake of Allah and for your sake. Verily, it was done for their sake and none of it was for Allah.”
Source: Sunan al-Dāraquṭnī 111
Grade: Sahih (authentic) according to Al-Albani
عَنِ الضَّحَّاكِ بْنِ قَيْسٍ الْفِهْرِيِّ قَالَ قَالَ رَسُولُ اللَّهِ صَلَّى اللَّهُ عَلَيْهِ وَسَلَّمَ إِنَّ اللَّهَ عَزَّ وَجَلَّ يَقُولُ أَنَا خَيْرُ شَرِيكٍ فَمَنْ أَشْرَكَ مَعِيَ شَرِيكًا فَهُوَ لِشَرِيكِي ثم قال يَا أَيُّهَا النَّاسُ أَخْلِصُوا أَعْمَالَكُمْ لِلَّهِ عَزَّ وَجَلَّ فَإِنَّ اللَّهَ لا يَقْبَلُ إِلا مَا أُخْلِصَ لَهُ وَلا تَقُولُوا هَذَا لِلَّهِ وَلِلرَّحِمِ فَإِنَّهَا لِلرَّحِمِ وَلَيْسَ لِلَّهِ مِنْهَا شَيْءٌ وَلا تَقُولُوا هَذَا لِلَّهِ وَلِوُجُوهِكُمْ فَإِنَّهَا لِوُجُوهِكُمْ وَلَيْسَ لِلَّهِ مِنْهَا شَيْءٌ
111 سنن الدارقطني كتاب الطهارة باب النية
2764 المحدث الألباني خلاصة حكم المحدث إسناده صحيح في السلسلة الصحيحة