Question

.............it is a document on the basis of which transaction are first recorded in the books​

Answer 1

Explanation:

The source document, on the basis of which the transactions are recorded in the Purchases Book, is called inward invoice, bill or credit memo. It is received by a firm from the supplier of goods when the credit purchases are made.

so,your answer is the source

I hope it's helpful

Answer 2

Answer:

$\huge\underline\red{Souce \: Documents}$

All business transactions are evidenced by an appropriate document such as invoice, memo, bill, receipt, cheque etc. Such document which provides complete information of the financial transactions to be recorded are known as source documents.