There is a chapter under citta vithi in Abhidhammattha Sangaha. In which of the seven books in Abhidhamma this concept appear?
As you mentioned, Chapter IV of the Sangaha describes citta vithi. The Visuddhimagga includes many partial references (look under "cognitive series" in the index) but no complete analysis. Clearly, the material in the Sangaha is a later development of what is found in the Visuddhimagga (perhaps 500 years earlier). The material in the Visuddhimagga is a later development of sporadic references found in the Patthana (Conditional Relations). For example, on page 72 of PTS Conditional Relations Vol II, it says, "advertance (avajjana) is related to five-fold consciousness through proximity condition". On page 74, it says, "Life-continuum (bhavanga) without applied thought but with sustained thought is related to advertance by proximity condition." Proximity condition (and contiguity condition) imply a process. In summary, the fully-worked-out version found in the Sangaha was developed from fragments found in the Visuddhimagga (and commentaries) and these were developed from even earlier (and much more primitive) fragments found in the Patthana.
This is first found in the Visuddhimagga. You should understand the difference between Sutta Abhidhamma vs Abhidhammatha Sanga ha.
This question came up in a Dhamma discussion which I was part of but I am not sure or have verified if this is valid.
Citta Vithi and Javana are found in the Abhidhamma Commentaries but not in the Abhidhamma Pitaka. I.e., it does not appear in the any of the 7 books.
In the same way what are the references to the concept of cuti patisandhi citta; ie. patisandhi citta conditioned by cuti citta in a minute fraction of a second. Is it also mentioned in pattana?. This is so important that by describing the mechanism of cuti patisandhi in this way only, the main teaching of that 'there is no sole' can be justified.
Vīthi is paṭṭhāna of abihdhamma-pitaka and the whole commentary, that were learned from buddha by sāriputta-mahāsāvaka then he author them in his phrase.
You must memorize paṭṭhāna in pali and learn it with the tipitaka memorizer, to prove that it is Vīthi.
If you doubt about abhidhamma's and commentary's history, please read this question: