Whoso faithfully admitted the Oneness of Allah, they also accepted the apostleship of Prophet Muhammad (May blessings of Allah be on him!) with their mind and tongue. They are always prominent in the execution of Allah’s orders. Such persons, shall not miss the proper ferry.
Verily you are (one) of the apostles . (252, Al-Baqarah).
Hence believe in Allah and His Apostle, the un-lettered Prophet, who believes in Allah and His discourses; and follow him so that you may be guided well (158, Al-Aaraf).
Note. Mere belief in the Oneness of Allah and the apostleship of the Prophet is not enough. A believer must affirm the same vocally i.e. by tongue.
Sarmad of Delhi used to utter لا اللهonly. When under the order of Emperor Aurangzeb he was asked to utter the full Kalima, he declined, saying that for the time being he was concerned with the fact that there was no Allah. He was, therefore, tried for disbelief and executed publicly. Faith is negatived by non-inclusion of the latter part in the Kalima, which is the reality and the law.

Those who in Lord's peerless Oneness believe,
Accept Muhammad's (P.B.U.H) guidance, with heart and speech,
Their's is abode of bliss, for they abide God's decree,
Never misled are they to paths that dubious be.

Those who in Lord's peerless oneness believe,
Accept Muhammad's (PBUH) guidance with heart and speech,
Their's is abode of bliss, for they abide God's decree
Never misled are they to paths that dubious be.

"He is the One and no one shares His Oneness" those who said this with firm faith,
And accept in heart and with tongue that Muhammad (PBUH) is the cause of creation,
In it decreed in Quran that they shall never stray to unfavorable landing.