Sumayyah Bint Khayaat (RA) was the first Believer to be martyred in Islam. She was tortured to death by Pagan Arabs, for declairing faith in the Oneness of Allah. A pagan Arab named Abu Jahl (father of ignorance) shoved a spear into her private parts.
Yasir Ben Amir (RA), husband of Sumayaah Bint Khayaat (RA), was the second Believer to be martyred in Islam. He was tortured to death by pagan Arabs, for declairing faith in the Oneness of Allah. He was tied to two horses and his body was ripped apart.
The first Muslims to recieve the good new of Jenna (Paradise), were Yasir (RA) and his family.
The Messenger of Allah (S) said to the first family of Martyrs: "O family of Yasir, bear this suffering patiently, for Allah has given you the promise of Jenna (Paradise)"- Al-Isabah
Ammar Ben Yasir (RA), son of Sumayyah Bint Khayyat (RA), was a Shi'a Muslim who supported Imam Ali ibn Abi Talib (AS). He was martyred in the Battle of Siffin, 650 C.E., while defending the House of Prophet Muhammad (S).
Sunni traditions report that Ammar Ben Yasir (RA) would be inviting them to Paradise
Sahih Bukhari, volume 1, Book 8 Number 438
Narrated 'Ikrima: The Prophet said: "May Allah be Merciful to Ammar. He will be inviting them to Paradise and they will be inviting him to Hell-Fire. Ammar said: 'I seek refuge with Allah from affliction.'"
Sunan Tirmidhi, Hadith Number 3800
Abu Huraira narrated that the Messenger of Allah said: "Rejoice Ammar, the transgressing party shall kill you."
Ammar Ben Yassir was martyred fighting against the Munafiqeen i.e. the internal enemies of Islam!
A Restatement of the History of Islam and Muslims, Sayed Ali Asgher Razwy
The first victims of pagan attrition and aggression were those Muslims who had no tribal affiliation in Makkah. Yasir and his wife, Sumayya, and their son, Ammar, had no tribal affiliation. In Makkah they were "foreigners" and there was no one to protect them. All three were savagely tortured by Abu Jahl and the other infidels. Sumayya, Yasir's wife, died while she was being tortured. She thus became the First Martyr in Islam. A little later, her husband, Yasir, was also tortured to death, and he became the Second Martyr in Islam.
Quraysh had stained their hands with innocent blood! In the roster of martyrs, Sumayya and her husband, Yasir, rank among the highest. They were killed for no reason other than their devotion to Allah and their love for Islam and Muhammad Mustafa. Those Muslims who were killed in the battles of Badr and Uhud, had an army to defend and to support them. But Yasir and his wife had no one to defend them; they bore no arms, and they were the most defenseless of all the martyrs of Islam. By sacrificing their lives, they highlighted the truth of Islam, and they built strength into its structure. They made the tradition of sacrifice and martyrdom an integral part of the ethos of Islam.
Bilal, Khabab ibn el-Arat, Suhaib Rumi, and other poor and unprotected Muslims were made to stand in the torrid sun, and were flogged by the infidels. Food and water were denied to them in the vain hope that hunger and thirst will compel them to abandon Muhammad and Islam