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Surah 3. Aal-Imran
Ayah 81 - 82
81وَإِذْ أَخَذَ ٱللَّهُ مِيثَـٰقَ ٱلنَّبِيِّـۧنَ لَمَآ ءَاتَيْتُكُم مِّن كِتَـٰبٍ وَحِكْمَةٍ ثُمَّ جَآءَكُمْ رَسُولٌ مُّصَدِّقٌ لِّمَا مَعَكُمْ لَتُؤْمِنُنَّ بِهِۦ وَلَتَنصُرُنَّهُۥ ۚ قَالَ ءَأَقْرَرْتُمْ وَأَخَذْتُمْ عَلَىٰ ذَٰلِكُمْ إِصْرِى ۖ قَالُوٓا۟ أَقْرَرْنَا ۚ قَالَ فَٱشْهَدُوا۟ وَأَنَا۠ مَعَكُم مِّنَ ٱلشَّـٰهِدِينَ
82فَمَن تَوَلَّىٰ بَعْدَ ذَٰلِكَ فَأُو۟لَـٰٓئِكَ هُمُ ٱلْفَـٰسِقُونَ
[81-82] Remember, Allah made this Covenant with His Messengers: "Now that We have given you the Book and Wisdom, you are hereby bound to believe in and help a Messenger,69 who comes to you afterwards, confirming the teachings you already possess." After this, He asked, "Do you confirm this and take up the heavy responsibility of your Covenant with Me?" They said, "Yes, we confirm." Then Allah said, "Very well, bear witness to this and I also bear witness with you. Now whosoever breaks the Covenant after this, he shall be a transgressor."70
69It implies this: "You people of the Book are bound by the Covenant of your own Prophets to believe in and help Muhammad (Allah's peace be upon him) for we entered into a compact with every Prophet to the effect that they (and their followers by implication) must help every Prophet sent by Us for the preaching and the establishment of the way of life for which they had been appointed. Therefore you should not have any prejudice against him, nor consider religion as your own monopoly; you should not oppose the Truth but come under the banner of anyone who raises it for this purpose.
It is interesting to note that according to Palmer (The Koran), "the Talmudic sources confirm that God assembled all past, present, and future Prophets on Mount Sinai and entered into the compact mentioned in the text."
In this connection it should also be clearly understood that this compact was taken from every Prophet before the advent of Hadrat Muhammad (Allah's peace be upon him); therefore every Prophet informed his followers about the Prophet coming after him and told them to follow him. But there is no mention in the Qur'an or in the Traditions that any such compact was taken from the Holy Prophet: nor did he inform his followers about the coming of any Prophet after him and believing in him. On the contrary, he categorically declared that he was the last in the line of Prophets.
70This implies that the people of the Book were breaking their covenant with Allah by rejecting Prophet Muhammad (God's peace be upon him) and opposing his mission; they were disregarding that covenant which their Prophets had made with Allah. Hence they were perverted transgressors who had gone beyond the limits imposed by Allah.