俱舍論頌疏論本 9.49

9.49

於三受因異，未了知名觸者，三受因者，謂三受境，境名為因，能生受也。謂出胎後三兩歲來，根、境、識三能有對觸，此位五蘊總名為觸，觸相顯故，故標觸名。於三受境未能了知，故未名受。

"When differences in the causes of the three feelings / are not yet understood, it is called contact": as for "the causes of the three feelings," this refers to the objects of the three feelings, for the objects are called causes because they can produce feeling. That is, after emerging from the womb up to two or three years of age, the faculty, object, and consciousness can have contact upon confronting one another; the five skandhas of this stage are collectively named contact. Because the characteristic of contact is prominent, it is designated with the name contact. Since one is not yet able to understand the objects of the three feelings, it is not yet called feeling.