The Prophet (peace and blessings be upon him) said:
"When you come (to the mosque), pray with the people (in congregation), even if you have already prayed (alone)."
Hadith Referenceصحیح الجامع الصغیر / حرف الألف / 467
Hadith Gradingالألبانی:صحيح
Hadith Takhrij[مالك الشافعي ن حب] عن محجن. صحيح أبي داود ٥٩٠.