Musnad Ahmad 129:4

Isma'il narrated to us, from Khalid al-Hadhdha', from Abu Qilabah, from Malik ibn al-Huwayrith, that the Prophet (peace and blessings of Allah be upon him) said to him and to a companion of his: "When the prayer time arrives, give the Adhan and the Iqamah." And he said once: "Then let the older of you two lead you in prayer." Khalid said: So I said to Abu Qilabah, "What about the recitation?" He said: "They were both close [in their level of knowledge]."