«فَإِنْ تَشَارَكَ الرَّاوِي وَمَنْ رُوِيَ عَنْهُ فِي أَمْرٍ مِنَ الأُمُورِ المُتَعَلِّقَةِ بِالرِّوَايَةِ»
“When the transmitter and the person from whom he narrates share some aspect connected with transmission.”
Narrating from one's qarīn—a fellow transmitter of comparable generation or standing—is called riwāyat al-aqrān. Peerhood is not restricted to an identical birth year; the relationship may be established through their common scholarly setting and opportunities for hearing.
For instance, Zayd and ʿAmr may have studied under the same teacher in a similar period. When Zayd later narrates something learned by ʿAmr, the chain may display transmission between peers.