1 Corinthians 15:58 says:
Therefore, my beloved brethren, be ye stedfast, unmoveable, always abounding in the work of the Lord, forasmuch as ye know that your labour is not in vain in the Lord.
and
Galatians 6:9 says:
And let us not be weary in well doing: for in due season we shall reap, if we faint not.