Sunan At-Tirmidhi

Abu Ishaq narrated from Ikrimah, from Ibn Abbas who said:“Abu Bakr [may Allah be pleased with him] said: ‘O Messenger of Allah! You have become gray.’ He said: ‘I have gone gray from (Surat) Hud, Al-Waqi`ah, Al-Mursalat and `Amma Yatasa'alun and Idhash-Shamsu Kuwwirat.’”