Is what is established in the obligatory prayer also established in the voluntary prayer, and vice versa?

The Shaykh : And he also asks you, what is your opinion? Is the obligatory prayer measured by the voluntary prayer, or the voluntary prayer by the obligatory one? If something is valid in the obligatory prayer, can it be transferred to the Sunnah, or not?

The questioner : This is the understanding of my question, which is seeking refuge with Allah from four things in the Sunnah. I want you to answer it for me.

The Shaykh : You did not answer me.

The questioner : I am asking; I do not know.

The Shaykh : Yes, that is the answer, you do not know. Now, what is known among all the scholars is that what is established in any prayer, even if something is established in the Sunnah, the obligatory prayer follows it, and vice versa, a fortiori, unless there is evidence that excludes or removes one prayer from another. In that case, the specific ruling is applied. So my first question was that it is established in the words of the Messenger (peace and blessings be upon him) that he used to seek refuge from four things, and we also add something else to this. But before that, so that we finish this, since he did that in the obligatory prayer, we have nothing preventing us from doing that in the Sunnah; because what is not legislated in this is not legislated in this except by specific evidence, for example, is it permissible for one who is able to stand to pray the voluntary prayers sitting, but the reverse is not? Why? The evidence for that has been established, okay?

The questioner: Yes.

The Shaykh : Yes, but the reverse: if something is established in the obligatory prayer, its like is permissible in the Sunnah, and the reverse of the reverse: if something is established in the Sunnah, its like is permissible in the obligatory prayer, except by evidence, as we mentioned earlier regarding standing. But regarding your question, we have a general evidence, which is his saying (peace and blessings be upon him): So, in this issue, two things are gathered and available for us: first, attaching the Sunnah to the obligatory prayer due to the absence of a preventer, and second, the generality of his saying (peace and blessings be upon him): So I think this is sufficient for answering your question, is it not?

The questioner : Yes, indeed.

The Shaykh : May Allah reward you with good. Yes.