Abu Salih narrates from Sayyiduna Uthman bin Affan (may Allah be pleased with him) that Sayyiduna Uthman (may Allah be pleased with him) was in Masjid al-Khayf and said: O people! I heard a hadith from the Messenger of Allah (peace and blessings be upon him) which I kept hidden from you, but now I am disclosing it as advice. I heard the Messenger of Allah (peace and blessings be upon him) say: "One day of striving in the path of Allah is equal to a thousand days, so let every person reflect for himself."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب السير / 18505