‘Abdullah ibn al-Mas’ood (may Allah be pleased with him) said,

حدث القوم ما رمقوك بأبصارهم, فاذا رأيت منهم فترة فانزع

“Narrate (hadith etc.) to the audience as long as they glance at you with their eyes, and if you see slackness from them then halt”

Source: al-Jaami’ lil Akhlaaq ar-Raawi 1/330