Abdullah bin al-Samit (may Allah have mercy on him) said: One of the rulers used to delay the prayer. I asked Abu Dharr (may Allah be pleased with him), and he struck my thigh and said: I asked my close friend, meaning the Prophet (peace and blessings be upon him), and he (peace and blessings be upon him) struck my thigh and said: "Offer the prayer at its proper time; then, if you find the people praying, pray with them as well, and do not say: I have already prayed, so I will not pray with you."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الصلاة / 3636