More and more people are asking about if the holy warrior, "Ayatollah Sheikh Nimr Al Nimr" was the "Nafse Zaki" as prescibed in the prophecies of return of Imam Mahdi a.s (May Allah hasten his reappearance).
To help out your curious mind. You'll witness the riwayats and hadiths related to "Nafse Zaki - Pure Soul".
Note: Before reading below, beware that the signs of reappearance isn't explicitly the result for the return of the Imam Mahdi a.s except the 5 that are obligatory.
1. On the 25th Zil-Hijjah the announcement will be made and the announcer killed (This is the blood of Nafse Zakiyya - pure soul, those whose blood will touch the Ka'ba and who is mentioned in numerous prophecies).
2. His blood will be avenged 2 weeks later when Imam(a.s.) will appear himself at the Ka'ba.
3. In the 13th volume of Bihar-ul-Anwar, Imam Al-Baqir(a.s.) is quoted as saying that "The Qaim (Imam Al-Mahdi(a.s.)) will send one of his companions to Makka and will ask him to inform them that I'm sent by so-and-so to you and that we are the merciful Ahlul-Bayt and the Store-house of 'Risalat' (religious guidance) and 'Khilafat' and we are the progeny of Muhammad(pbuh&hf) and from the time that the Prophet of Islam(pbuh&hf) left this world until now, we've been oppressed and deprived and our rights have been usurped. So we call you to befriend us. When that young man will utter these words, he will be caught and beheaded between 'Rukn' and 'madam' (in Masjidul Haram) and this young man is the 'Nafse Zaki'.......... And between the death of the 'Nafse Zaki' and the re-appearance of Imam Al-Mahdi (A.S.) there will not be a gap of fifteen nights".
4. Nafs-e-Zakiyyah is a person by the name of Muhammad ibn al-Hasan (Allama Majlisi. Bihar al-Anwar 52)
5. He is a descendant of Husayn ibn Ali (Allama Majlisi. Bihar al-Anwar 52)
6. Duty of Nafs-e-Zakiyyah is mentioned in a hadith that narrated by Abu-Basir from Muhammad al-Baqir. According to the hadith when Muhammad al-Mahdi realizes, people of Mecca don't accept his reappearance. Therefore, he will send Nafs-e-Zakiyyah as an envoy to convey his oral message to people of Mecca (Majlisi, Muhammad Baqir. Bihar al-Anwar 52. p. 307)
7. He will be slayed by people of Mecca around the Ka'ba after impart Imam's message to them. (Hashemi Shahidi, Seyyed Asadullah. Introduce of promised person. Jamkaran Mosque Publication. p. 524.)
8. It will rise from the west; a pure soul (nafs zakiyya) will be killed in the outskirts of Kufa with seventy righteous men; a Hashimite will be slaughtered between the corner (of the Ka'ba) and the station of Abraham)
9. As well, before the advent of the Imam, a noble person will be killed during the Hajj rites in Makkah. In the traditions, this person has been referred to as the Pure Soul or an-Nafs al-Zakiyyah.
10. Upon the death of Nafs-e-Zakiyya, a voice will resonate from the skies declaring, “Be aware that your ruler is the Mahdi who shall fill the earth with truth and justice.” (Eqdud-Durar) (http://www.islamicinsights.com/religion/signs-of-the-return.html)
11. Five signs will be seen before the uprising of the Qaim: Arrival of the Yemenite man, Sufyani, Call from the sky, Sinking of the ground in Baidha desert and Killing of the Pure Soul (Nafse Zakiyyah).”
12. (Bihar Al Anwar Vol-51-52-53-( the-Promised-Mahdi-English v 13 -Translation ) Chapter Thirty book II, Ikmaaluddin- Shaykh Saduq)
13. After that Imam Mahdi (a.s.) would arise and his standard would be held by Shuaib bin Salih. When Syrians realize that their country has come under the rule of the descendant of Abu Sufyan they would go to Mecca. Nafse Zakiyyah and his brother would be killed at that time.
14. Nafse Zakiyyah (the pure soul) is a young man from the Progeny of Muhammad (s.a.w.s.), his name is Muhammad bin Hasan, who would be killed without any crime and sin and when they slay, him they shall neither have any excuse in the heavens nor would they have any friend in the earth. At that time the Almighty Allah will send the Qaim of Aale Muhammad with a group that in the view of the people would be softer than antimony.
15. Imam Ja'far Sadiq (a.s.) said: And mutual discord in Bani so-and-so is inevitable, killing of Nafse Zakiyya is inevitable and the rising of Imam Qaim is also inevitable.
16. "When Nafse Zakiyyah (pure person) will be killed, a voice from the sky will declare, ‘Your leader is so and so!’ Then Mahdi will rise and will fill the earth with justice and equity." (Ammare Yasir)
Summarizing the Ahadith/Riwayats mentioned above:
1. There are 2 nafs-e-Zakiyya mentioned in the riwayats i.e one would be killed in Kufa (Iraq) and the other would be killed in Saudi (Hijaz)
2. The Nafs-e-Zakiyya is not a name but a nick name meaning (A pure soul).
3. Nafs-e-Zakiyya name would be "Muhammad ibn al-Hasan"
4. Killing of Nafs-e-Zakiyya is among the 5 major signs of reappearance of the Imam Mahdi a.s
5. He would be Syed Hashmi (from the progeny of Prophet Mohammad s.a) (Ayatollah Nimr is not a Syed but a Sheikh)
6. Nafs-e-Zakiyaa would call upon people to introduce the Ahlulbayt but he would be killed for this.
7. Imam Mahdi a.s would rise right after 15 days of killing of Nafs-e-Zakiya.
I've collected the above Signs from several websites. Thus the Ahadith mentioned may be Sahih or Zaieef (Strong or weak respectively)
Hope you would conclude it on your own.