It is narrated from a companion from Jahina (may Allah be pleased with him) that I asked the Prophet Muhammad (peace and blessings be upon him), "When should I perform the Isha prayer?" The Prophet Muhammad (peace and blessings be upon him) said, "When the night has covered every valley."
Hadith Referenceمسند احمد / مسند الأنصار رضي الله عنهم / 23095
Hadith Gradingحکم دارالسلام:إسناده ضعيف لجهالة عبدالعزيز ابن عمرو