«كان يجلس إذا صعد المنبر حتى يفرغ المؤذن ثم يقوم فيخطب ثم يجلس فلا يتكلم ثم يقوم فيخطب»
It was the practice of the Prophet (peace and blessings be upon him):
"When he (peace and blessings be upon him) ascended the pulpit, he would sit until the mu'adhdhin finished the call to prayer. Then he would stand and deliver the sermon, then sit and not speak, then stand and deliver the sermon again."
Hadith Referenceصحیح الجامع الصغیر / حرف الكاف / 4913