The Companions of Allaah’s Messenger (صلّى الله عليه وسلّم) suffered the worst forms of torture because of their adherence to the correct ‘aqeedah, and their making all worship purely and sincerely for Allaah alone, and their rejection of shirk and kufr.
From ’Abdullaah ibn Mas’ood, radiyallaahu ‘anhu, who said, “The first people to openly proclaim their Islaam were seven: Allaah’s Messenger (صلّى الله عليه وسلّم) , Aboo Bakr, ’Ammaar and his mother Sumayyah, Suhayb, Bilaal and al-Miqdaad. So as for Allaah’s Messenger (صلّى الله عليه وسلّم) , Allaah gave him protection through his uncle Aboo Taalib. As for Aboo Bakr, Allaah gave him protection through his people. But as for the rest of them, the Mushriks would take hold of them and dress them in iron armour and place them to scorch and roast in the sun. There was not one of them except that they responded to them except Bilaal, for his soul became as nothing to him for Allaah’s sake, and his people had no respect for him. So they gave him to the children who used to drag him around the streets of Makkah and he would say repeatedly, ‘(He who has the right to worship is) One, One.’”
In the Seerah of Ibn Hishaam  there occurs: ’Umayyah ibn Khalf used to take him (Bilaal) out in the midday heat of the sun, and throw him down upon his back, on the ground of the flat valley bed of Makkah, and he would order for a large rock to be placed on his chest. Then he would say, “By Allaah, you will stay like this until you die, unless you disbelieve in Muhammad (صلّى الله عليه وسلّم) and you worship al-Laat and al-’Uzzaa.” So he would say, whilst he was in that condition, “(He who alone has the right to worship is) One, One.”
Sumayyah was tortured until death because of the ‘aqeedah of tawheed not becasue she was a political leader. So from Mujaahid who said, “The first martyr in Islaam was Sumayyah the mother of ’Ammaar. Aboo Jahl thrust a spear into her abdomen.”
Ibn Sa’d said, “She accepted Islaam early on in Makkah and she was one of those who was tortured to force them to abandon their religion. But she bore and endured it until Aboo Jahl came to her and thrust a spear into her abdomen and she died.”
 Reported by al-Haakim in al-Mustadrak (3/284) and he declared it saheeh and adh-Dhahabee mentioned it in Siyar A’laamin-Nubalaa (1/348) and he said, “It has a saheeh chain of narration…”
 Seerah of Ibn Hishaam (1/318).
 At-Tabaqaat of Ibn Sa’d (8/264/265). He said, “Ismaa’eel ibn ’Umar, Abul-Mundhir related to us that Sufyaan ath-Thawree narrated to us from Mansoor from Mujaahid who said…” This is a saheeh chain of narration to Mujaahid.
 Tabaqaat Ibn Sa’d (8/264).
The above is excerpted from the book : “The Methodology of the Prophets in Calling to Allaah – that is the way of wisdom and intelligence” – by Shaykh Rabee’ ibn Haadee al-Madkhalee hafidhahullaah, translated by Dawud Burbank rahimahullah