Source of quotation from Buddhaghosa about Buddha being trackless Radhakrishnan's edition of The Dhammapada provides the following quotation from Buddhaghosa as a commentary on Verse 179 (Chapt, 14, 1 Buddhavagga) where the Buddha is described as apadam trackless/signless:


  "The man who is possessed of even a single one of such conditions as
  raga, attachment, &amp;c., him ye can lead forward; but the Buddha has not even one condition or basis of renewed existence, and therefore by
  what track will you lead this unconditioned Buddha?"


Could anyone tell me the source of this quotation and also provide me with the Pali?
Radhakrishnan is not a wholly reliable guide to the Dhammapada. One must read him with care. The Pāḷi is


  Kena padenāti yassa hi rāgapadādīsu ekapadampi atthi, taṃ tumhe tena
  padena nessatha. Buddhassa pana ekapadampi natthi, taṃ apadaṃ buddhaṃ tumhe kena padena nessatha. Dhammapada Aṭṭhakathā, 3.196.


It's from Buddhaghosa's commentary on the Dhammapada (Dhammapada Aṭṭhakathā). This section comments on the words "by what pada" (kena padena). My rough translation is:


  If he has even one from amongst the padas such as desire (rāga), then he can be led by that pada. But the Buddha has not even one of them, the Buddha is without a pada, there is no pada by which you can lead him.


The question then is what pada means here. If we read this along with Dhp 180 then it becomes clear that pada means desire etc (rāgapadādi). And it seems to me that "track" is a poor translation of pada here. It does not convey that in this context pada is referring to desire etc. I suggest that "sign" is somewhat better, but that even this is less than entirely satisfactory. Only the context can help us in this case. 

In what sense craving is a "path" or a "track" or even a "sign" is moot. But then these verses are rather esoteric and a simple answer might be misleading anyway.