It is narrated from Sayyiduna Buraydah al-Aslami (may Allah be pleased with him) that the Messenger of Allah (peace and blessings be upon him) was on one of his military expeditions, and he (peace and blessings be upon him) said: "On a cloudy day offer the Asr prayer early, for (because of the weather one may not notice the time passing, and) whoever abandons the Asr prayer, his deeds are nullified."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الصلاة / 2091