The truth that permits neither falsehood nor hypocrisy. The evidence of the truth is Allah (عز و جل )’s saying:

“Alif Lam Mim. Do people think that they will be left alone because they say: “We Believe”, and will not be tested. And we indeed tested those who were before them. And Allah will certainly make (it) known (the truth of) those who are true, and will certainly make (it) known (the falsehood of) those who are liars, (although Allah knows all that before putting them to test).” [Al-Ankabut 29:1-3]

Also:

“And of mankind, there are some (hypocrites) who say: “We believe in Allah and the Last Day” while in fact they believe not. They (think to) deceive Allah and those who believe, while they only deceive themselves, and perceive it not! In their hearts is a disease (of doubt and hypocrisy) and Allah has increased their disease, A painful torment is theirs because they used to tell lies.” [Al-Baqarah 2:8-10]

It was narrated by Mu’adh ibn Jabal (رضي الله عنه ) that Prophet Muhammad (صلى الله عليه و سلم ) said:
“There is none who testifies truthfully from his heart that there is no deity worthy of worship except Allah and Muhammad (صلى الله عليه و سلم ) is His abd (His worshipper) and Messenger, except that Allah will save him from Hell-Fire.” [Reported by Al-Bukhari]

Regarding His saying: “And of mankind, there are some (hypocrites) who say: “We believe in Allah and the Last Day.”
Allah (عز و جل ) informs us about what the hypocrites used to do i.e. to show their Iman (faith) by (merely) pronouncing it (with their tongues) whilst their hearts concealed Al-Kufr (Disbelief). They thought that they could deceive Allah (عز و جل ), and deceive the believers into being misled by them and inclined towards them. The opposite was the result for this deceit. They were in fact deceiving themselves but did not know because of their utter ignorance and their evil conscience. What drove them to this deceit and lying was suspicion.
As for their penalty in the Hereafter, it is in His, the Exalted’s, saying: “…A painful torment is theirs because they used to tell lies.”

Referring to the hadith quoted earlier narrated by Mu’adh ibn Jabal (رضي الله عنه ) that the Prophet (صلى الله عليه و سلم ) said:

“There is none who testifies…” It was reported by Al-Bukhari and Muslim that Anas (رضي الله عنه ) narrated from Mu'adh (رضي الله عنه ), the text of which states in Al-Bukhari that the Prophet (صلى الله عليه و سلم ), when Mu'adh (رضي الله عنه ) was alongside him as a companion rider, said:
“O Mu'adh ibn Jabal, “Mu'adh replied: “Labbaik, O Messenger of Allah and Sa’daik.” The Prophet (صلى الله عليه و سلم ) said: O Mu'adh! he replied: ‘Labbaik, O Messenger of Allah and Sa’daik’, three times. The Prophet (صلى الله عليه و سلم ) said: “There is none who testifies truthfully from his heart, that there is no deity worthy of worship except Allah and that Muhammad is the Messenger of Allah, except that Allah will save him from the Hell-Fire”. (Mu'adh) asked: “O Messenger of Allah, should I not inform the people about it so that they may have glad tidings?” The Prophet (صلى الله عليه و سلم ) replied: “When the people hear about it they will solely depend upon it.”
Mu'adh (رضي الله عنه ) narrated this Hadith just before his death- fearing that he may be committing a sin by withholding knowledge from the people.

This confirms that the Hadith agrees with the Ayat (verses) which I quoted earlier that the testimony will not be accepted unless oral testification (by word of mouth) is joined and accompanied by firm belief of the heart. Allah has falsified the hypocrites and did not accept their testimony although they announced to the Prophet (صلى الله عليه و سلم ) that he is the Messenger of Allah. That is because they merely said it by word of mouth and were not truthful. Regarding this Allah(عز و جل ) said:

When the hypocrites come to you (O Muhammad), they say “We bear witness that you are indeed the Messenger of Allah. “Allah knows that you are indeed His Messenger and Allah bears witness that the hypocrites are liars indeed.” [Al-Munafiqun 63:1]