There is another hadith about Hazrat ‘Umar that the ulema use in their support and that needs our attention. The full hadith is as follows:
The translation of the first part of the hadith which is generally cited is the following:
‘Uqbah bin ‘Amir (may Allah be pleased with him) reports that “The Messenger(sa) of Allah said: ‘If there was to be a Prophet after me, it would certainly have been ‘Umar bin al-Khattab.’”
The second part of the hadith which gives the commentary of Imam Tirmidhi on the above statement is conveniently disregarded. Imam Tirmidhi adds after the above citation:
This hadith falls in the category of the weak ones [da‘if ]. We do not find it anywhere except through Mishrah bin Ha‘an. (Tirmidhi vol. 2, Abwabul-Manaqib Babo Manaqib-e-‘Umar(ra)).
Our opponents argue that according to this hadith since Hazrat ‘Umar(ra) lived after the Holy Prophet(sa) and did not become a Prophet, therefore, prophethood has ended.
It is to be noted that after recording this hadith, Imam Tirmidhi observed that it should fall in the category of ‘hasanun gharibun’—authenticity of this hadith is questionable. It is handed down by one narrator, Mishrah bin Ha‘an. At-Tahdhib At-Tahdhib, an authentic work of research about the narrators, includes a note about Ha‘an in volume 10, page 155:
Ibn Hayyan states: ...He (Mishrah bin Ha‘an) was among the weak narrators of hadith. He is not to be relied upon. In particular when he is found to be the lone narrator of a hadith the hadith should be rejected. (At-Tahdhib At-Tahdhib, by Ibn Hajar al-‘Asqalani)
Hadith-e-Gharib means exactly that; that there is a lone narrator.
Ibn-e-Dawud, agreeing with the above view, further states in even stronger terms:
He [Mishrah bin Ha‘an] was in the gang of al-Hajjaj who had besieged ‘Abdullah bin Zubair and had raided the Ka‘bah and pelted it with stones.
In view of the above, the authenticity of this hadith is totally shattered.
There are, however, sayings of the Holy Prophet(sa) which may help clarify this topic. The Holy Prophet(sa) is reported to have said to Hazrat ‘Umar (may Allah be pleased with him):
Had I not been raised as a Prophet, O ‘Umar, you would have been raised as one. (Mirqat al-Masabih Sharhu Mishkatil-Masabih, vol. 10, p. 403)
Another saying reads:
Had I not been sent to you, ‘Umar would have been sent to you. (Kunuzul-Haqa’iq by Imam ‘Abdur-Ra’uf al-Manawi, vol. 2, p. 74)
All these traditions point to one fact. That is, Hazrat ‘Umar(ra) was endowed with the potential of prophethood. Had the Holy Prophet(sa) not been born and commissioned, Hazrat ‘Umar (may Allah be pleased with him) would have been. This is the meaning of these sayings. Ba‘di has been used in the sense of 
‘ghairi’—other than me.