Musnad Ahmad 1017:61

Zayd ibn Hubab narrated to us, Husayn ibn Waqid narrated to me, Abdullah ibn Buraydah narrated to me, he said: I heard my father, Buraydah, saying: The Messenger of Allah (peace and blessings of Allah be upon him) was delivering a sermon to us, when al-Hasan and al-Husayn came, wearing two red shirts, walking and stumbling. The Messenger of Allah (peace and blessings of Allah be upon him) descended from the pulpit, carried them, and placed them in front of him. Then he said: "Allah and His Messenger have spoken the truth: 'Your wealth and your children are but a trial' [At-Taghabun: 15]. I looked at these two boys walking and stumbling, and I could not be patient until I interrupted my speech and lifted them up."