Rajab of Mudar?

﷽

The Sacred Months are mentioned by implication in the Quran, but their names are not given. Their names are mentioned in the Sunnah:

Abu Bakrah (may Allah be pleased with him) reported that the Prophet (peace and blessings of Allah be upon him) gave his Farewell Sermon and said:

“Time has completed its cycle and is as it was on the Day when Allah created the heavens and the earth. The year is twelve months, of which four are sacred, three consecutive months – Dhu’l-Qa’dah, Dhu’l-Hijjah and Muharram – and the Rajab of Mudar which comes between Jumaada and Sha’baan.”

(Reported by al-Bukhari, no. 1741, in [Kitaab] al-Hajj, 
al-Khutbah Ayaam Mina; and by Muslim, 
no. 1679, in [Kitaab] al-Qisaamah, Baab Tahreem al-Dimaa’)

It was called Rajab of Mudar because [the tribe of] Mudar did not tamper with its timing, unlike the rest of the Arabs, who used to tamper with the months and change their order depending on whether they were in a state of war or not. This was the postponing referred to in the aayah (interpretation of the meaning):

“The postponing (of a Sacred Month) is indeed an addition to disbelief: thereby the disbelievers are led astray, for they make it lawful one year and forbid it another year in order to adjust the number of months forbidden by Allah, and make such forbidden ones lawful.”

[al-Tawbah 9:37]

It was also said that the reason why it was attributed to Mudar was because they venerated it and respected it so much, so it was attributed to them.