Mus'ab bin Sa'd narrates from his father, Sayyiduna Sa'd (may Allah be pleased with him); al-A'mash (may Allah have mercy on him) said: I know it only as being from the Prophet (peace and blessings be upon him): "Moderation is better in every matter, except in the matter of the Hereafter."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الشهادات / 20803