It is narrated from Sayyiduna Ka'b bin Malik (may Allah be pleased with him) that the Messenger of Allah (peace and blessings be upon him) came out to a group of the Ansar who were spreading pebbles in a mosque, and he (peace and blessings be upon him) said: "Make it spacious; you will fill it."
Hadith Referenceالمعجم الكبير للطبراني / باب الكاف / 16231