SB 1.3.7

dvitīyaṁ tu bhavāyāsya
 rasātala-gatāṁ mahīm
uddhariṣyann upādatta
 yajñeśaḥ saukaraṁ vapuḥ
Word for word: 
dvitīyam — the second; tu — but; bhavāya — for the welfare; asya — of this earth; rasātala — of the lowest region; gatām — having gone; mahīm — the earth; uddhariṣyan — lifting; upādatta — established; yajñeśaḥ — the proprietor or the supreme enjoyer; saukaram — hoggish; vapuḥ — incarnation.
Translation: 
The supreme enjoyer of all sacrifices accepted the incarnation of a boar [the second incarnation], and for the welfare of the earth He lifted the earth from the nether regions of the universe.
Purport: 

The indication is that for each and every incarnation of the Personality of Godhead, the particular function executed is also mentioned. There cannot be any incarnation without a particular function, and such functions are always extraordinary. They are impossible for any living being to perform. The incarnation of the boar was to take the earth out of Pluto’s region of filthy matter. Picking up something from a filthy place is done by a boar, and the all-powerful Personality of Godhead displayed this wonder to the asuras, who had hidden the earth in such a filthy place. There is nothing impossible for the Personality of Godhead, and although He played the part of a boar, by the devotees He is worshiped, staying always in transcendence.