Sayyiduna Nafi' (may Allah have mercy on him) narrates from Sayyiduna Ibn Umar (may Allah be pleased with them both) that when we found someone absent from the Fajr and Isha prayers, our opinion of him would be bad.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الصلاة / 4954
Hadith Gradingمحدثین:صحيح لغيره
Hadith Takhrij«صحيح لغيره۔ الطبراني في الكبير 13085»