Epaphras, who is one of you, a servant of Christ, saluteth you, always labouring fervently for you in prayers, that ye may stand perfect and complete in all the will of God.
--Colossians 4:12
Prayer done right is work. Effectual prayer entails effort, albeit spiritual effort, but effort none the less. The Book of Mormon prophet Enos "wrestled" before the Lord in his mighty prayer (Enos 1:2) When I read the words that Ether prayed as he asked for help in lighting the barges he had built to cross the ocean to the promised land, I hear him struggle with great effort to beseech God for a blessing. When Jesus knelt with the Nephites to pray with them, He "groaned within himself" as He began his prayer, indicating the tremendous effort He exerted as He prayed for His people.
God approves of work, and He Himself also works. He rested on the seventh day from the work of creation (see Genesis 2:2). Isaiah prophesied God would do a "marvelous work and a wonder" (see Isaiah 29:14), which work and wonder we see today in the Book of Mormon, the restoration of the true Church of Christ, and the gathering of Israel. God works in us and through us (see Ephesians 3:2, Philippians 2:13, Colossians 1:29). He works constantly, and He expects me to work as well.
Prayer is a good work, but it is nevertheless work.