Complaining is not a sin God takes lightly, for it shows that you are not happy with the plan God has for your life. The Bible calls it many things including; murmuring, grumbling, disputing and vain babbling. This is a sin everyone deals with from time to time. We need to confess it, turn from it, and be content, knowing God is in control. 

(Phil 2:14) Do all things without murmurings and disputings.

(2 Tim 2:16) But shun profane and vain babblings: for they will increase unto more ungodliness.

(1 Cor 10:10) Neither murmur ye, as some of them also murmured, and were destroyed of the destroyer.

(Eph 4:29) Let no corrupt communication proceed out of your mouth, but that which is good to the use of edifying, that is may minister grace unto the hearers.

(Rom 14:19) Let us therefore follow after the things which make for peace, and things wherewith one may edify another.

(Eph 5:3-4) Says foolish talking is something we are to avoid.

(Ps 39:1) I said, I will take heed to my ways, That I sin not with my tongue: I will keep my mouth with a bridle, While the wicked is before me.

(Prov 21:23) Whoso keepeth his mouth and tongue Keepeth his soul from troubles.

(Ps 141:3) Set a watch, O LORD, before my mouth; keep the door of my lips.

     There were numerous times in the Bible when the Israelites complained while in the desert. It angered God each time, and He punished them a number of times for it. These serve as an example of how complaining displeases God.

(Num 11:1) And when the people complained, it displeased the Lord: and the Lord heard it; and his anger was kindled; and the fire of the Lord burnt among them, and consumed them that were in the uttermost parts of the camp.

(Num 12) Aaron and Miriam complained against Moses and God gave Miriam leprosy for 7 days.

(Num 14:26-38) The people complained and God did not allow any of that generation to enter the Promised Land.

(Num 16) The people complained twice, and the ground opened up and swallowed some, then a plague was sent and it killed 14,700 people.

(Num 21:4-6) The people complained about a lack of food and water and about the bread God miraculously sent from heaven and God sent fiery serpents among the people that bit them and many died.

     Thank the Lord for His forgiveness through Jesus for sins such as complaining. Let us guard our tongue and speak things which will bring glory to God and build our testimony to others of the blessings God has given us.