Assalaamu alaykum. If I take a meal when the sun has come up, can I still participate in the voluntary fast? I look forward to your response. May Allaah reward you.

All perfect praise be to Allah, The Lord of the worlds. I testify that there is none worthy of worship except Allah and that Muhammad, sallallaahu ‘alayhi wa sallam, is His slave and Messenger.

As long as you ate after the break of dawn (the Fajr), then it is invalid to perform a voluntary fast for the rest of that day. The condition for the validity of the voluntary fast based on intention during the daytime (meaning that the person did not have the intention to fast before dawn) is to not have consumed any food or drink nor have engaged in any act that invalidates the fast before holding the intention to fast on that day.

Ibn Qudaamah wrote, “As for fasting, the intention is one of its conditions or pillars; it is inconceivable that a fast could be valid unless its conditions or pillars are present. One of the conditions of it is that the fasting person had not eaten anything before holding the intention of (voluntarily) fasting nor done any of the acts that invalidate the fast. If he does any of those acts, his voluntary fast is invalid, and no scholar held a different view in this regard.”

Allah knows best.