Is it true that only one sect of the Ummah will enter paradise?

Anas (may God be pleased with him) narrated that the Messenger of God (peace and blessings be upon him) said: "My ummah [community] will divide into 70 or 70 something groups; all of them will be in Jannah [Paradise] except for the unbelievers" [Recorded by Ad-Dailami in his Musnad Al-Firdaws, and by Abu Ya'la and others.

Scholarly opinions
In his book Ahsan At-Taqasim, Mohammed ibn Ahmed Al-Bishari al-Maqdisi enumerated these groups and mentioned the two different phrasings of the hadith which read as "72 groups will be in paradise and one in Hellfire" and "72 groups will be in Hell-fire and one will be saved [from Hell-fire]". Then, he said: "The second wording of the hadith is well-known while the first has the more authentic chain of transmission."

For this reason, ibn al-Wazir contested the hadith in general and the additional statement of "72 will be in Hell-fire and one will be saved [from Hell-fire]" in particular. This is because not only does the additional phrase result in misguidance among the people of the ummah, but also leads to accusations of kufr [disbelief].

In his book Al-'Awasim, ibn al-Wazir (may God have mercy on him) spoke about the excellence of this ummah and warned against any involvement in accusing any Muslim of disbelief. He said: "Do not be misled by the [phrase] "all of them will be in Hell-fire except for one" because it is an invalid and baseless addition and it is not far-fetched [to say] that it has been introduced by atheists."

He also quoted ibn Hazm who said: "This addition is fabricated, it is neither classified as mawquf [attributed to any of the Companions] nor as marfu' [raised to the Prophet]. All the hadiths reported on disparaging the Qadariya, Murji'a and 'Ash'ariya groups are likewise weak."

Some past and present scholars have refuted this hadith based on its chain of transmission while others based their refutation on its meaning and text. For example, Abu Mohammed ibn Hazm refuted the allegations of those who accuse others of disbelief due to differences in belief and based his refutation on some evidences which they mentioned in this respect. Abu Mohammed mentioned two hadiths used as proof by those who accuse others of disbelief and which they falsely attribute to the Messenger of God (peace and blessings upon him and family). These are:
1- "The Qadariya and Murji'a are the magus of this ummah”.

"This ummah will divide into 70 or 70 something groups; all of them will be in Hell-fire except one which will be in Jannah."

In his commentary on the two previously mentioned hadiths, Abu Mohammed said: "In the first place, their chains of transmission are unauthentic. Any hadith with an unauthentic ascription cannot be used as proof according to the opinion of the hadith scholars who recognize the hadiths with khabar al-wahid. So, what then of those who do not recognize it!?"

In his book Al-'Awasim wa Al-Qawasim, The Yemeni Jurist, imam and supporter of the sunnah, Mohammed ibn Ibrahim al-Wazir, reconciled intellectual and textual evidences and enumerated the hadiths narrated by Mu'awiyah (may God be pleased with him) including the 8th hadith on the ummah dividing into 70 something groups all of which will be in Hell-fire except for one. He commented: "The chain of transmission of this hadith includes a nasibi [i.e. a Shi'ite person who hates the Sunnis] and thus the hadith is unauthentic." At-Tirmidhi reported the same hadith through Abdullah ibn 'Amr ibn al-'As (may God be pleased with them both) and said: "It is a gharib [singular] hadith. At-Tirmidhi mentioned this hadith in the book Iman through al-Ifriqi whose name is Abd al-Rahman ibn Ziyad ibn Abdullah ibn Yazid. Ibn Majah narrated a similar hadith on the authority of 'Awf ibn Malik and Anas. Abu Mohammed said that all these narrations do not meet the conditions of the hadith Sahih; therefore, Bukhari and Muslim did not record them. At-Tirmidhi authenticated the hadith narrated by Abu Huraira through Mohammed ibn 'Amr ibn 'Alqama which does not include "All of them will be in Hellfire except for one ". Ibn Hazm said: "The author of Al-Badr al-Munir mentioned that this additional statement is fabricated.”

• Commenting on the words of God,or to confuse you [so you become] sects and make you taste the violence of one another. [Al-An'am, 65]

Ibn kathir wrote in his Tafsir: "It was reported in a hadith with multiple chains of transmissions that the Prophet (pbuh) said: "This ummah will divide into 73 sects, all of them will be in Hellfire except for one." Ibn Kathir did not add anything to the hadith and he did not classify it either as authentic or fair although he elaborated on the interpretation of the verse by mentioning the hadiths and non-prophetic narrations related to it.

Imam al-Shawkani mentioned ibn Kathir's opinion on the above hadith and said, "As for the additional phrase "all of them will be in Hell-fire except for one", some hadith scholars have maintained that it is weak. Ibn Hazm, on the other hand, maintained that it is fabricated.

Despite the fact that some scholars have declared this hadith fair [hasan] like ibn Hajar or authentic [Sahih] like Sheikh al-Islam ibn Taymiya due to its multiple chains of transmission, it does not stand as proof on the division of the ummah, both in manner and number, to be considered of permanent application until the day of Judgment. The existence of such sects at any given time, suffices as proof for the authenticity of the hadith. Some of these sects may exist and, when they do, they will be overwhelmed by truth and then perish, never to return.

This is exactly what happened to many of such deviant sects, some of which have perished and are no more.

This hadith indicates that all of these sects are attributed to the Prophet's ummah—i.e. Muslims. This is proved by his words: "my ummah will divide" and means that despite their deviation, these sects do not leave the religion of Islam nor are they been omitted from the Muslim community.

And the fact that they will be in (Hellfire) does not mean that they will be among its eternal dwellers like the disbelievers but will be dealt with like the disobedient believers. One of the pious believers, angels or Prophets may intercede for them (by the leave of God) or they may have made good deeds or suffered calamities which may obliterate their sins and ward off torture.
God may forgive them by His grace and bounty especially if they did their best in arriving at the truth, but failed and deviated from the right path. God has forgiven people of this ummah their mistakes, forgetfulness and anything they were forced to do.