Sayyidah Aishah (may Allah be pleased with her) said that the Prophet (peace and blessings be upon him) ordered mosques to be built in the neighbourhoods, and said: "They should be kept pure and clean and be perfumed."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الصلاة / 4308
Sayyiduna Samurah (may Allah be pleased with him) wrote to his sons that the Prophet (peace and blessings be upon him) used to command us to build mosques in our towns, and used to say: "Build them properly and keep them pure."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الصلاة / 4309
Abu al-Walid asked Ibn Umar (may Allah be pleased with them both): How did the use of saffron perfume in the mosque begin? He said: The Prophet (peace and blessings be upon him) came into the mosque and saw phlegm in the mosque on the qiblah side. He (peace and blessings be upon him) said: "Something other than this would be better." A man heard this, so he brought saffron; he scraped it off and rubbed saffron in its place. He (peace and blessings be upon him) said: "This is better than the first," and then the people did the same.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الصلاة / 4310
Sayyiduna Abu Hurayrah (may Allah be pleased with him) said that the Prophet (peace and blessings be upon him) missed a black woman who used to clean the mosque. He (peace and blessings be upon him) asked: "Where is so-and-so?" The people said: She has died.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الصلاة / 4311