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
Muhammad bin Ka'b (may Allah have mercy on him) says: Do not say 'Ramadan', for Ramadan is one of the names of Allah Almighty; rather, say 'the month of Ramadan'.
This has also been narrated from Mujahid and al-Hasan al-Basri, but the chain to them is weak. Muhammad bin Isma'il al-Bukhari, in his Sahih, used the following hadith as evidence that this (saying 'Ramadan') is permissible.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الصيام / 7905
Sayyiduna Abu Hurayrah (may Allah be pleased with him) says that the Messenger of Allah (peace and blessings be upon him) said: "When Ramadan comes, the gates of Paradise are opened, the gates of Hell are closed, and the devils are chained." Al-Bukhari (may Allah have mercy on him) said: And the Prophet (peace and blessings be upon him) said: "Whoever fasts Ramadan", and he also said: "Do not precede Ramadan (by fasting before it)."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الصيام / 7906