Reference: Siyar A’laam an-Nubalaa – Volume 4, Page 359
al-Haarith al-Ghanawee said:
Riba’ee ibn Hiraash took an oath that his teeth would not be seen when laughing, until he knew where he was destined. And one of those who washed his body, said he was still smiling as he lay on his bed while they were washing him, until they had finished; may Allaah have mercy upon him.