In the Holy Quran it is written that Muhammad (PBUH) said:
“If they (Jews and Christians) had observed the Torah and the Gospel and that which was revealed unto them from their Lord, they would have enjoyed happiness from every side. Among them there are people on the right course but many of them are of evil conduct.”
(Quran 5:66)
Further;
Say, "O People of the Scripture, you are [standing] on nothing until you uphold [the law of] the Torah, the Gospel, and what has been revealed to you from your Lord." And that which has been revealed to you from your Lord will surely increase many of them in transgression and disbelief. So do not grieve over the disbelieving people.
(Quran 5:68)
It would appear Muslims are commanded in the Quran 4:136, to believe in the books God revealed to the Jews and the Christians.
O you who have believed, believe in Allah and His Messenger and the Book that He sent down upon His Messenger and the Scripture which He sent down before. And whoever disbelieves in Allah, His angels, His books, His messengers, and the Last Day has certainly gone far astray.
Yet most Muslims believe the Torah and Gospel the Jews and Christians hold in their possession to be corrupted and not the Torah and Gospel Muhammad spoke of.
Is the Gospel and Torah the Christians and Jews possessed in the time of Muhammad so different from today that it could be considered corrupted? If the Gospel and Torah was corrupted in Muhammad’s day, why is this never mentioned in the Quran?