Sayyiduna Abu Hurayrah (may Allah be pleased with him) says that the Messenger of Allah (peace and blessings be upon him) said: "Do not say 'Ramadan, Ramadan', for Ramadan is one of the names of Allah; rather, say 'the month of Ramadan'."
Abu Ma'shar is Najih al-Sindi; Yahya bin Ma'in declared him da'if (weak), and Yahya al-Qattan did not narrate from him, while Abd al-Rahman bin Mahdi did narrate from him; and Allah knows best. It has also been said that it is from Abu Ma'shar, from Muhammad bin Ka'b, as his own saying, and that is more likely.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الصيام / 7904