Ibn Ishaq محمد بن إسحاق بن يسار‎ · The Book on Hajj

"The Messenger of Allah permitted the camel herders who were in the camp (at Mina) to stone on the Day of An-Nahr then to gather the stoning of two days after the Day of An-Nahr, so that they stoned them during one of them." Malik said: "I think that he said about the first of them: 'They they should stone on the day of departure.'"