Sayyiduna Abu Qatadah (may Allah be pleased with him) said that he (peace and blessings be upon him) came to some of the Ansar who were building a mosque for themselves. He (peace and blessings be upon him) said: "Make it so spacious that you can all fit in it."
There is disagreement over the chain of this hadith.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الصلاة / 4306