Musannaf Ibn Abi Shayba 17:1077

Narrated to us Abd al-Rahim ibn Sulayman, from Isma'il, from Husayn, from Muhajir ibn Qunfudh, who said: We were speaking with him when three people passed by on a donkey. He said to the last of them, "Get down, may Allah curse you." It was said to him, "Do you curse this person?" He said, "We have been forbidden from this: that three people ride upon one beast."