Within a few days of the Prophet's(sa) arrival in Medina, the pagan tribes there became interested in Islam and a majority of them joined. Many, not persuaded at heart, also joined. In this way a party joined the fold of Islam who were not Muslims at heart. Its members played a very sinister part in subsequent history. Some of them became sincere Muslims. Others remained insincere and kept intriguing against Islam and Muslims. Some refused to join at all. But they could not stand the growing influence of the New Faith, so they migrated from Medina to Mecca. Medina became a Muslim town. In it was established the worship of the One God. There was not a second town in the world then which could make this claim. It was no small joy to the Prophet(sa) and his friends that within a few days of their migration a whole town had agreed to give up the worship of idols and to establish instead the worship of the One Invisible God. But there was no peace yet for Muslims. In Medina itself a party of Arabs had only outwardly joined Islam. Inwardly, they were the sworn enemies of the Prophet(sa). Then there were the Jews, who continuously intrigued against him. The Prophet(sa) was aware of these dangers. He remained alert and urged his friends and followers to be on their guard. He often remained awake the whole night (Bari, Vol. 6, p. 6o). Tired by night-long vigilance he once expressed a desire for help. Soon he heard the sound of armour. "What is this?" he asked. "It is Sa’d bin Waqqas(ra), O Prophet(sa), who has come to do sentinel duty for you" (Bukhari and Muslim). The people of Medina were alive to their great responsibility. They had invited the Prophet(sa) to come and live in their midst and it was now their duty to protect him. The tribes took counsel and decided to guard the Prophet's(sa) house in turn.
In the unsafety of his person and in the absence of peace for his followers, there was no difference between the Prophet's(sa) life at Mecca and his life at Medina. The only difference was that at Medina Muslims were able to worship in public in the mosque which they had built in the name of God. They were able to assemble for this purpose five times in the day without let or hindrance.
Two or three months passed. The people of Mecca recovered from their bewilderment and started making plans for the vexation of Muslims. They soon found that it did not fulfil their purpose merely to trouble Muslims in and around Mecca. It was necessary to attack the Prophet(sa) and his followers at Medina and turn them out of their new refuge. Accordingly they addressed a letter to Abdullah bin Ubayy ibn Salul, a leader of Medina, who, before the Prophet's(sa) arrival, had been accepted as king of Medina by all parties. They said in this letter that they had been shocked at the Prophet's(sa) arrival at Medina and that it was wrong on the part of the people of Medina to afford refuge to him. In the end they said:
Now that you have admitted our enemy in your home, we swear by God and declare that we, the people of Mecca, will join in an attack on Medina unless you, the people of Medina, agree to turn him out of Medina or give him a joint fight. When we attack Medina, we will put to the sword all able-bodied men and enslave all women (Abu Dawud, Kitab al-Kharaj).
Abdullah bin Ubayy ibn Salul thought this letter a God-send. He consulted other hypocrites in Medina and persuaded them that if they allowed the Prophet(sa) to live in peace among them they would invite the hostility of Mecca. It behoved them, therefore, to make war upon the Prophet(sa), if only in order to appease the Meccans. The Prophet(sa) got to know of this. He went to Abdullah bin Ubayy ibn Salul and tried to convince him that such a step would prove suicidal. Many people in Medina had become Muslims and were prepared to lay down their lives for Islam. If Abdullah declared war upon Muslims, the majority of the people of Medina would fight on the side of Muslims. Such a war would, therefore, cost him dear and spell his own destruction. Abdullah, impressed by this advice, was dissuaded from his plans.
At this time, the Prophet(sa) took another important step. He collected the Muslims and suggested that every two Muslims should become linked together as two brothers. The idea was well received. Medinite took Meccan as his brother. Under this new brotherhood, the Muslims of Medina offered to share their property and their belongings with the Muslims of Mecca. One Medinite Muslim offered to divorce one of his two wives and to have her married to his Meccan brother. The Meccan Muslims declined to accept the offers of the Muslims of Medina out of regard for the needs of the latter. But the Muslims of Medina remained insistent, and the point had to be referred to the Prophet(sa). The Muslims of Medina urged that the Meccan Muslims were their brothers; so, they had to share their property with them. The Meccan Muslims did not know how to manage land. But they could share the produce of the land if not the land itself. The Meccan Muslims declined with thanks this incredibly generous offer, and preferred to stick to their own vocation of trade. Many Meccan Muslims became rich again. But Muslims of Medina always remembered their offer to share their property with Meccan Muslims. Many a time when a Medinite Muslim died, his sons divided the inheritance with their Meccan brothers. For many years, the practice continued, until the Qur’an abolished it by its teaching about the division of inheritance (Bukhari and Muslim).