Bilal (may Allah be pleased with him) was mercilessly persecuted by his master. Umayya bin Khalaf who was the worst enemy of Islam, would make him lie down on the burning sand at mid-day and would place a heavy stone on his chest so that he could not move even a limb. He would then say to him: Renounce Islam or swelter and die in this state. Even under these afflictions Bilal would exclaim: Ahad (the One Allah) Ahad (the One Allah). At last Abu Bakr freed Bilal from Umayya.
Dear Muslims, when Bilal was asked how he endured all these tortures and pain, he remarked that his belief in Allah covered all the pains. It's like a glass of milk. If you put water into the glass of milk, the water takes the colour of the milk. The same way, when Bilal was tortured, his faith overcame the pain.