That he be mindful, along with citing the evidence.

The Shaykh : We mentioned the second condition, which is that he be mindful, and its opposite is forgetfulness. If a person forgets and eats or drinks, his fast is valid. What is the evidence?
The student:

The Shaykh : This is a general evidence, and there is a specific evidence from Abu Hurayrah that the Prophet (peace and blessings be upon him) said: This is a specific evidence that explicitly addresses the issue. However, it is obligatory, my brothers, it is obligatory in the case of ignorance: if he becomes aware of the reality, he must abstain. And in the case of forgetfulness: if he remembers, he must abstain. And here is a question.