Brahmin Dona is walkiing along behind the Buddha when he notices the mark of the Wheel in gotama's footprints. Drawing near he asks Gotama about what sort of being he may be and is told that he is beyond 'being' and is Buddha.
Read the Sutta
Index to available translations: AN 4.36
There are a couple of interesting things about this sutta aside from the lesson. First: though the Arahant is said to be 'trackless' here Dona is able to see his footprints.
The commentary aparently attempts to explain that the footprints are invisible, but that this Brahman can 'see'.
This is exactly backwards of the essence of the meaning of 'trackless'.
Trackless should be understood as a matter of leaving no traces indicating that anything that was done by the 'trackless' one has been done from lust, hate, or stupidity. It is not a matter of leaving no footprints.
The need to make Gotama into a supernatural being is to miss the real magic in what Gotama realized.
The other thing is that Woodward speculates that this is the Dona to whom was given the Buddha's bowl on his death. I wonder what happened to this bowl?
Bhk. Thanissaro notes [AN 4.36.than#n2] that there is a great deal of discussion (see notes in both the Bhk. Bodhi and Woodward translations (notes are missing from the Bhk. Bodhi versions permitted to be published on line)) concerning the use of the future tense in Dona's inquiries.
Bhk. Thanissaro's solution here is that this is a manner of speech.
I would only express it slightly differently as a contracted form of: "Will you be being about being a ..."
From the perspective of the awakened mind there is actually no true 'present' to base a present tense upon in the case of asking a person what he is in the present. Things are under constant change, so a being is always about becoming something. There should really be a special tense for this case: The present-future or the future-present.