Is it true what is said that Bilal (may Allah be pleased with him) used to say "أسهد" (Ash-had) instead of "أشهد" (Ash-had) in the Athan, and that the Prophet (peace be upon him) said: "Bilal's 'seen' (س) is a 'sheen' (ش) with Allah Almighty"?

What some common people believe, that Bilal ibn Rabah (may Allah be pleased with him) used to pronounce the letter 'shīn' as 'sīn' in the Athan, and that the Messenger of Allah (peace be upon him) said: "Bilal's 'sīn' is a 'shīn' to Allah Almighty," has no basis. Indeed, Bilal (may Allah be pleased with him) was among the most eloquent of people and had the most beautiful voice.