No one can be a believer until they acknowledge all the Messengers.
Allah is the One Who sent the Messengers and rejecting even one of them is tantamount to rejecting them all. The gravest sin is disbelief in Allah and the denial of His revelations. Thus, admission to Paradise necessitates faith in every Messenger.
So, everyone must believe in all the Messengers appointed by Allah. This faith remains incomplete without acknowledging and adhering to the teachings of the last Messenger, Prophet Muhammad (peace be upon him).
Allah states in His Holy Book that rejecting any of His Messengers is tantamount to rejecting both Allah and His revelation.
Read, if you may, the following verse:
"إنَّ الَّذِينَ يَكْفُرُونَ بِاللَّهِ ورُسُلِهِ ويُرِيدُونَ أنْ يُفَرِّقُوا بَيْنَ اللَّهِ ورُسُلِهِ ويَقُولُونَ نُؤْمِنُ بِبَعْضٍ ونَكْفُرُ بِبَعْضٍ ويُرِيدُونَ أنْ يَتَّخِذُوا بَيْنَ ذَلِكَ سَبِيلًاأُولَئِكَ هُمُ الكافِرُونَ حَقًّا وأعْتَدْنا لِلْكَفَرَيْنِ عَذابًا مُهِينًا﴾"."Those who disbelieve in Allah and His messengers and wish to make a distinction between Allah and His messengers, and they say, "We believe in some and disbelieve in others," wishing to adopt a way in between.* It is they who are the true disbelievers, and We have prepared for the disbelievers a humiliating punishment."
[4: 150,151].
