Praise be to Allah,
Sufyaan narrated to us from [Muhammad] ibn al-Munkadir who said that he heard Jaabir ibn ‘Abdullaah say,
“A Bedouin came to Allah’s Messenger (peace and blessings of Allah be on him), embraced Islam and swore allegiance to him, pledging to migrate [to Madeenah]. But soon he fell sick with a fever. He went to the Prophet (peace and blessings of Allah be on him) and said, ‘Cancel my pledge.’ ‘I will not cancel it,’ the Prophet replied. The Bedouin came again and said, ‘Cancel my pledge.’ The prophet (peace and blessings of Allah be on him), replied, ‘I will not cancel it.’ Then he came back again and said, ‘Cancel my pledge.’ ‘I will not cancel it,’ the Prophet (peace and blessings of Allah be on him) replied. The Bedouin then ran away and the prophet (peace and blessings of Allah be on him), said, “Madeenah is like a pair of bellows: it expels its impurities and purifies its good.”
(Musnad Allmad, Vol. 3 , p. 307. The isnaad of this Hadeeth is Saheehh according to the conditions set by al-Bukhaaree and Muslim)
Migration to Madeenah was obligatory before the Prophet (peace and blessings of Allah be on him) returned victoriously to Makkah in the year 8 AH, but not so after this event.
A bellows is a mechanical device that blows a strong current of air; used to make a fire burn more fiercely.
This is a characteristic of Madeenah not only during the time of the Prophet but during every generation until the Day of Judgment. The Prophet also said, “The Hour will not be established until Madeenah has expelled the evil ones among its dwellers.” This is in reference to the time when the earth will shake around Madeenah at the coming of the Dajjaal (False Messiah), who will not be allowed to enter it, and all the hypocrites will abandon Madeenah to meet him. (Ref. Noor-ud-Deen abul-Hasan as-Samhoodee, Khulaasat al Wajaa bi Akhbar Daar al-Mustafaa, p.ll)
Thulaathiyyaat Musnad Ahmad ibn Hanbal (may Allah have mercy on him)
Reports of Imaam Ahmad that have only three narrators between him and the Prophet, peace, and blessings be upon him.
Shaykh Muhammad ibn Ahmad ibn Saalim as–Saffaareenee al–Hanbalee ~(1114 –1188 AH)