Abu Abdullah al-Hafiz (may Allah have mercy on him) informed us: I asked Abu Zakariyya al-Anbari (may Allah have mercy on him), and he narrated to us from Abu Abdullah al-Bushanji (may Allah have mercy on him) concerning shortening the salam, that he said: One does not draw out the salam; rather, he shortens it.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الصلاة / 2992