Muwatta Malik, Book 15, Hadith 24 (USC-MSA) ⓘ

Yahya related to me from Malik that Ziyad ibn Abi Ziyad said that Abu'd-Darda had said, "Shall I not tell you the best of your deeds, and those that give you the highest rank, and those that are the purest with your King, and are better for you than giving gold and silver, and better for you than meeting your enemy and striking their necks?" They said, "Of course." He said, "Remembrance (dhikr) of Allah ta ala."

وَحَدَّثَنِي عَنْ مَالِكٍ، عَنْ زِيَادِ بْنِ أَبِي زِيَادٍ، أَنَّهُ قَالَ قَالَ أَبُو الدَّرْدَاءِ أَلاَ أُخْبِرُكُمْ بِخَيْرِ، أَعْمَالِكُمْ وَأَرْفَعِهَا فِي دَرَجَاتِكُمْ وَأَزْكَاهَا عِنْدَ مَلِيكِكُمْ وَخَيْرٍ لَكُمْ مِنْ إِعْطَاءِ الذَّهَبِ وَالْوَرِقِ وَخَيْرٍ لَكُمْ مِنْ أَنْ تَلْقَوْا عَدُوَّكُمْ فَتَضْرِبُوا أَعْنَاقَهُمْ وَيَضْرِبُوا أَعْنَاقَكُمْ قَالُوا بَلَى ‏.‏ قَالَ ذِكْرُ اللَّهِ تَعَالَى ‏.‏ قَالَ زِيَادُ بْنُ أَبِي زِيَادٍ وَقَالَ أَبُو عَبْدِ الرَّحْمَنِ مُعَاذُ بْنُ جَبَلٍ مَا عَمِلَ ابْنُ آدَمَ مِنْ عَمَلٍ أَنْجَى لَهُ مِنْ عَذَابِ اللَّهِ مِنْ ذِكْرِ اللَّهِ ‏.‏