Sayyiduna Abu Hurayrah (may Allah be pleased with him) says that the Prophet (peace and blessings be upon him) said: "Do you not see that when a person dies, his eyes stay fixed (open)?" They said: Certainly, O Messenger of Allah, that is how it is. He (peace and blessings be upon him) said: "That is when his sight follows his soul."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الجنائز / 6608