The preposition (à, de or none) is dictated by the verb.

A couple of issues 

1. I think you are referring to seeing no preposition, de or à preceding ne pas (several examples in the lesson) - in the form of (conjugated verb) {no preposition/de/à} [ne pas infinitive], rather than {ne pas} (followed by de or à) [infinitive], as the point of your question

2. It is the conjugated verb that precedes [ne pas infinitive] that determines whether no preposition/de/à is needed - as per the lists of verbs that require à or de before an infinitive. https://www.lawlessfrench.com/grammar/verbs-with-de/ https://www.lawlessfrench.com/grammar/verbs-with-a/

Thank you for the explanation and the links. Are there any lessons that teach when de or à are needed or is this something that just needs to be memorized?

Erica, there is no easy way to ‘predict’ the verb-preposition combinations. There are many good reference sites with lists of verbs requiring à or de,  such as those I linked above, but you will tend to acquire the commonly used verbs naturally as you read and practise French. 

Maartin's link on this question is very helpful along with other inks in that lesson.  https://www.lawlessfrench.com/grammar/verbs-with-de/ https://www.lawlessfrench.com/grammar/verbs-with-a/

I would like to add it to my notebook, but on my subscription page, I can't find it.  Is there a way to do this?

Maartin's link on this question is very helpful along with other inks in that lesson.  https://www.lawlessfrench.com/grammar/verbs-with-de/ https://www.lawlessfrench.com/grammar/verbs-with-a/

I would like to add it to my notebook, but on my subscription page, I can't find it.  Is there a way to do this?

Maartin's link on this question is very helpful along with other inks in that lesson.  https://www.lawlessfrench.com/grammar/verbs-with-de/ https://www.lawlessfrench.com/grammar/verbs-with-a/

I would like to add it to my notebook, but on my subscription page, I can't find it.  Is there a way to do this?