It is narrated from Hazrat Abu Dharr (may Allah be pleased with him) that once the Holy Prophet (peace and blessings be upon him) said: O Abu Dharr! What will your condition be when you live among people who delay the prayer from its appointed time? Then he said: You should perform the prayer at its proper time. If you have to join them, then perform the prayer again with them (with the intention of nafl). Do not say, "I have already performed the prayer, so I will not perform it now."