حَدَّثَنَا عَبْدُ اللَّهِ بْنُ مُحَمَّدٍ الزُّهْرِيُّ، حَدَّثَنَا سُفْيَانُ، عَنْ مِسْعَرٍ، عَنْ وَبَرَةَ، قَالَ سَأَلْتُ ابْنَ عُمَرَ مَتَى أَرْمِي الْجِمَارَ قَالَإِذَا رَمَى إِمَامُكَ فَارْمِ ‏.‏ فَأَعَدْتُ عَلَيْهِ الْمَسْأَلَةَ فَقَالَ كُنَّا نَتَحَيَّنُ زَوَالَ الشَّمْسِ فَإِذَا زَالَتِ الشَّمْسُ رَمَيْنَا ‏.‏
Translation
Narrated Wabrah

I asked Ibn 'Umar: When should I throw pebbles at the Jamar? He replied: When your imam throws pebbles, then throw. I repeated the question to him, and he said: We used to wait for the sun to pass the meridian, and when the sun passed the meridian, we would throw pebbles.