Abu al-Zinad (may Allah have mercy on him) relates: I heard Kharijah bin Zayd (may Allah have mercy on him); he used to criticise those imams who, after giving the salam to end the prayer, would remain sitting just as they were in the prayer, and he would say: The sunnah way in this matter is that the imam gets up after giving the salam.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الصلاة / 3002