Mishkat al-Masabih 10 The Rites of Pilgrimage كتاب المناسك 151

وَعَن وَبرةَ قَالَ: سَأَلْتُ ابْنَ عُمَرَ: مَتَى أَرْمِي الْجِمَارَ؟ قَالَ: إِذَا رَمَى إِمَامُكَ فَارْمِهِ فَأَعَدْتُ عَلَيْهِ الْمَسْأَلَةَ. فَقَالَ: كُنَّا نَتَحَيَّنُ فَإِذَا زَالَتِ الشَّمْسُ رمينَا. رَوَاهُ البُخَارِيّ

Wabara said he asked Ibn ‘Umar when he should throw pebbles at the jamras , to which he replied, “Throw them when your imam does so.” He repeated the question and received the reply, “We used to wait for the proper time, and when the sun passed the meridian we threw them.” Bukhari transmitted it.