“斋戒沐浴” can be translated into English as "fast and bathe" or "observe a fast and take a bath".
“斋戒” is often translated as “fast” (referring to abstaining from food, especially for religious or spiritual purposes).
“沐浴” is simply “bathe” or “take a bath”.
In a more detailed or context-specific translation, you might also say something like "perform religious abstinence and purification rituals" to capture the full cultural and religious significance of the phrase, though this is longer and less literal. The simpler “fast and bathe” is often sufficient in many contexts.