Musannaf Ibn Abi Shaybah

Hazrat Maymoon says that a man asked Hazrat Abu Dharr, "I have not heard you mention fasting; what is the reason for this?" He replied, "Fasting is certainly a meritorious act, but not here." That is, in some situations, other deeds have greater reward than fasting, such as jihad, etc. Similarly, sometimes not fasting during travel becomes more virtuous.