allah the almighty said in the qur'an:
and [recall, o people of the scripture], when allah took the covenant of the prophets, [saying], "whatever i give you of the scripture and wisdom and then there comes to you a messenger confirming what is with you, you must believe in him and support him." [allah] said, "have you acknowledged and taken upon that my commitment?" they said, "we have acknowledged it." he said, "then bear witness, and i am with you among the witnesses." and whoever turned away after that – they were the defiantly disobedient. (3:81-82)
ali ibn abi talib (may allah be pleased with him) and his cousin, ibn `abbas (may allah be pleased with him), both said, " allah the almighty did not send a single prophet except that he took from him the promise that if allah the almighty should send muhammad pbuh during his lifetime he would believe in him and support him; and he ordered him to take the pledge from his nation that if muhammad was sent while they were alive they would believe in him and support him." as-suddi related something similar.
and allah the almighty quoted the supplication of prophet ibraheem:
"our lord, and send among them a messenger from themselves who will recite to them your verses and teach them the book and wisdom and purify them. indeed, you are the exalted in might, the wise." (2:129)
ibn katheer commented: " allah the almighty mentions the invocation of ibraheem pbuh for the people of the haram [in makkah] asking that he send among them a messenger from themselves, i.e., from the descendants of ibraheem pbuh. this invocation was according to what allah the almighty had predestined concerning the appointment of muhammad pbuh as a messenger among the gentiles, to them and to all other races of mankind and jinn.
imam ahmad related from `al-irbaadh ibn sariah that the messenger of allah said,
"i was to allah the seal of the prophets while adam was still clay, and i shall inform you of its beginning: it was the supplication of my ancestor, ibraheem, tidings of me from `isa, son of maryam and the dream which my mother saw; that is what the mothers of prophets see in dreams."
he pbuh continued to be mentioned among the people until the seal of the prophets of bani isra'eel, `isa, pbuh spoke his name when he stood and addressed them, saying,
"indeed i am the messenger of allah to you confirming what came before me of the torah and bringing good tidings of a messenger to come after me, whose name is ahmad." (61:6)
that is why the hadith said,
"the supplication of my ancestor, ibraheem and tidings from `isa, son of maryam."
the mention of his excellent qualities and deeds in the early scriptures are confirmed by the words of allah the almighty:
those who follow the messenger, the unlettered prophet, whom they find written in what they have of the torah and the gospel, who enjoins upon them what is right and forbids them what is wrong and makes lawful for them the good things and prohibits for them the evil and relieves them of their burden and the shackles which were upon them. (7:157)
`ataa ibn yasaar reported: i met `abdullah ibn `amr ibn al-`aas (may allah be pleased with him) and said, "inform me about the description of allah's messenger in the torah." he said, "yes, by allah, he is described in the torah with the same description as in the qur'an:
o prophet, indeed we have sent you as a witness and a bringer of good tidings and a warner, (33:45) and also as a sanctuary for the gentiles.
[allah said:] 'you are my servant and my messenger; i have called you al-mutawakkil (the dependant on allah).' he is not rude or harsh, nor is he noisy in the marketplaces. he does not compensate a bad deed with another; rather, he pardons and forgives. allah will not cause him to die until he has amended the altered religion through him with their saying, 'la ilaha ill-allah.' blind eyes, deaf ears and closed hearts will be opened by him." (al-bukhari)
al-bayhaqi narrated from ibn `abbas (may allah be pleased with him): "al-jarud ibn `abdullah (may allah be pleased with him) came and accepted islam. he said to the prophet pbuh, 'by him who sent you with the truth, i found your description in the gospel. the virgin's son (i.e., jesus son of mary) gave tidings of you.'"
and abu musa al-ash`ari (may allah be pleased with him) reported that an-najashi said, "i testify that muhammad is the messenger of allah and that the one who gave tidings of him was jesus. if not for my preoccupation with the affairs of the kingdom and the responsibility i carry for the affairs of my people, i would have come to him to carry his shoes." (abu dawud)
another name of prophet muhammad pbuh.
 difficulties in religious practice.
extreme measures previously required for repentance.