A narration of Mujaahid states that the other Muslims were made to wear coats of steel armour and then left to swelter in the sun. They therefore suffered terribly from the combined heat of the sun and the scorching armour. When night fell, Abu Jahal would come to them with his spear and start taunting and threatening them.
Another narration of Hadhrat Mujaahid states that the Mushrikeen used to lead Hadhrat Bilaal Radiallahu Anhu through the two mountains of Makkah with a rope around his neck. (1)
Hadhrat Urwa bin Zubayr Radiallahu Anhu narrates that Hadhrat Bilaal Radiallahu Anhu was a slave of a lady from the Banu Jumh tribe. The Mushrikeen used to torture him on the burning sands of Makkah, making him lie flat on the hot sand (and place a heavy rock on his chest) so that he should commit Shirk. However, he would continuously say, "Ahad! Ahad!" When Waraqa (bin Naufal, the cousin of Hadhrat Khadeeja Radiallahu Anha) would pass as Hadhrat Bilaal Radiallahu Anhu was being tortured, he would say, "Ahad, Ahad, 0 Bilaal (Allaah is certainly One). (Addressing the Mushrikeen, he would say) By Allaah! If you kill this man, I shall definitely make his grave a place of attracting Allaah's blessings and mercy." (2)
Hadhrat Urwa Radiallahu Anhu narrates that when Waraqa bin Naufal used to pass by Hadhrat Bilaal Radiallahu Anhu as he was being tortured and calling out "Ahad" ("Allaah is One"), he would say, "Allaah is One, 0 Bilaal." Waraqa bin Naufal would then turn to Umayyah bin Khalaf who was responsible for torturing Hadhrat Bilaal Radiallahu Anhu and say, "I swear by Allaah that if you kill this man, I shall definitely make, his grave a place of attracting Allaah's blessings and mercy."
Eventually, when Hadhrat Abu Bakr Radiallahu Anhu passed by one day as the Mushrikeen were torturing Hadhrat Bilaal Radiallahu Anhu, he said to Umayyah, "Do you not fear Allaah for (what you are doing to) this poor man? Until when will you continue?" Umayyah said, "It is you who had landed him into this trouble. You may rescue him from this treatment you are witnessing." Hadhrat Abu Bakr Radiallahu Anhu said, "I am prepared to do so. I have an Abyssinian slave who is stronger than him and more steadfast on your religion. I shall give him to you in exchange for this man."
When Umayyah accepted the proposal, Hadhrat Abu Bakr Radiallahu Anhu said, 'You have a deal." Hadhrat Abu Bakr Radiallahu Anhu then gave Umayyah the slave and after taking possession of Hadhrat Bilaal Radiallahu Anhu, set him free. Before migrating to Madinah,
Hadhrat Abu Bakr Radiallahu Anhu set free seven slaves besides Hadhrat Bilaal Radiallahu Anhu for the pleasure of Allaah. (3)
A narration of Ibn Is'haaq states that when the afternoon heat grew intense, Umayyah would take Hadhrat Bilaal Radiallahu Anhu outside and throw him down on the burning sands of Makkah. He would then command others to place a heavy rock on the chest of Hadhrat Bilaal Radiallahu Anhu and say to him, 'You shall be left like this until you die or reject Muhammad and worship Laat and Uzza!" Despite his extreme suffering, Hadhrat Bilaal Radiallahu Anhu would continuously say, "Ahad! Ahad!"
Due to the torture that Hadhrat Bilaal Radiallahu Anhu and the others suffered and about how Hadhrat Abu Bakr Radiallahu Anhu freed them, Hadhrat Abu Bakr Radiallahu Anhu received the title of "Ateeq" from Rasulullaah Sallallahu Alayhi Wasallam, meaning "The one freed from Jahannam"
(1) Ibn Sa'd (Vo1.2 Pg.166).
(2) Zubayr bin Bakkaar as quoted in Isaaba (Vo1.3 Pg.634)
(3) Abu Nu'aym in Hilya Vol 1, Pg. 148)