(a) Abu Bakr bin Abdullah bin Qays narrates from his father (may Allah be pleased with him) that the Messenger of Allah (peace and blessings be upon him) said: "Whoever prays the two cool prayers will surely enter Paradise."
(b) Some grammarians say that 'ghudwatan wa 'ashiyyan' means morning and evening.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الصلاة / 2186