It was narrated that Al-Fadl bin Abbas said: "The Messenger of Allah (ﷺ) said to the people when they moved on the evening of Arafat and the morning of Jam' (assembly at Al-Muzdalifah): 'You must have tranquility.' He was reining in his camel, and when he entered Mina, he came down to Muhassir and said: 'You have to pick up pebbles the size of date stones of fingertips with which to stone the Jamrat.' And he (Al-Fadl) said: 'And the Prophet (ﷺ) gestured with his hand like a man throwing a pebble.'"
Source: sunnah.com
Other translations
Arabic
أَخْبَرَنَا عُبَيْدُ اللَّهِ بْنُ سَعِيدٍ، قَالَ حَدَّثَنَا يَحْيَى، عَنِ ابْنِ جُرَيْجٍ، قَالَ أَخْبَرَنِي أَبُو الزُّبَيْرِ، عَنْ أَبِي مَعْبَدٍ، عَنْ عَبْدِ اللَّهِ بْنِ عَبَّاسٍ، عَنِ الْفَضْلِ بْنِ عَبَّاسٍ، قَالَ قَالَ رَسُولُ اللَّهِ صلى الله عليه وسلم لِلنَّاسِ حِينَ دَفَعُوا عَشِيَّةَ عَرَفَةَ وَغَدَاةَ جَمْعٍ " عَلَيْكُمْ بِالسَّكِينَةِ " . وَهُوَ كَافٌّ نَاقَتَهُ حَتَّى إِذَا دَخَلَ مِنًى فَهَبَطَ حِينَ هَبَطَ مُحَسِّرًا قَالَ " عَلَيْكُمْ بِحَصَى الْخَذْفِ الَّذِي تُرْمَى بِهِ الْجَمْرَةُ " . قَالَ وَالنَّبِيُّ صلى الله عليه وسلم يُشِيرُ بِيَدِهِ كَمَا يَخْذِفُ الإِنْسَانُ .
sunnah.com