A Baptist once asked me "Are the seven Catholic Sacraments biblical?". My response is "Absolutely!". First let's look at what those seven sacraments are. They are Baptism, Confirmation, Eucharist, Penance, Anointing the Sick (Extreme Unction), Holy Orders and Matrimony. Now let's discuss what a "sacrament" is.
From the Catechism of the Catholic Church #1084 (in part) "...The sacraments are perceptible signs (words and actions) accessible to our human nature. By the action of Christ and the power of the Holy Spirit they make present efficaciously the grace that they signify." And #1116 "Sacraments are "powers that comes forth" from the Body of Christ, which is ever-living and life-giving. They are actions of the Holy Spirit at work in his Body, the Church. They are "the masterworks of God" in the new and everlasting covenant."
The sacraments are gifts from God and all were instituted by Jesus Christ. No man on earth, not even a Pope can change a sacrament because he has no authority to do so. Christ instituted them and so they stand until He comes again exactly how he founded them. To alter them would make it invalid. For example, a valid baptism is done with water. If the water element was changed to orange juice it would invalidate the Sacrament of Baptism. Christ instituted the element of water for Baptism and man cannot change that. Time to get back to the original question from the Baptist "Are the seven Catholic Sacraments biblical?". Yes, they are and while there are many scriptures for the sacraments I will give a few for each but these are by no means the only scriptures available for each of the sacraments.
-Matt.3:16 "As soon as Jesus was baptized, he went up out of the water. At that moment heaven was opened, and he saw the Spirit of God descending like a dove and lighting on him."
-Matt. 28:19 "Therefore go and make disciples of all nations, baptizing them in the name of the Father and of the Son and of the Holy Spirit,"
-Mk 1:8 "I baptize you with water, but he will baptize you with the Holy Spirit."
-John 3:5 "Jesus answered, "I tell you the truth, no one can enter the kingdom of God unless he is born of water and the Spirit."
Confirmation-John 14:16 "And I will ask the Father, and he will give you another Counselor to be with you forever—"
-Acts 2:4 "All of them were filled with the Holy Spirit and began to speak in other tongues as the Spirit enabled them."
-Heb.6:2 "instruction about baptisms, the laying on of hands, the resurrection of the dead, and eternal judgment."
-Matt.26-29 "26While they were eating, Jesus took bread, gave thanks and broke it, and gave it to his disciples, saying, "Take and eat; this is my body." 27Then he took the cup, gave thanks and offered it to them, saying, "Drink from it, all of you. 28This is my blood of the covenant, which is poured out for many for the forgiveness of sins. 29I tell you, I will not drink of this fruit of the vine from now on until that day when I drink it anew with you in my Father's kingdom."
-Luke 24:35 "Then the two told what had happened on the way, and how Jesus was recognized by them when he broke the bread."
-John 6: 51 "I am the living bread that came down from heaven. If anyone eats of this bread, he will live forever. This bread is my flesh, which I will give for the life of the world."
-John 6 "53Jesus said to them, "I tell you the truth, unless you eat the flesh of the Son of Man and drink his blood, you have no life in you. 54Whoever eats my flesh and drinks my blood has eternal life, and I will raise him up at the last day. 55For my flesh is real food and my blood is real drink. 56Whoever eats my flesh and drinks my blood remains in me, and I in him."
Penance-Matt. 16:19 "I will give you the keys of the kingdom of heaven; whatever you bind on earth will be bound in heaven, and whatever you loose on earth will be loosed in heaven."
-John 20:21-23 "Again Jesus said, "Peace be with you! As the Father has sent me, I am sending you." 22And with that he breathed on them and said, "Receive the Holy Spirit. 23If you forgive anyone his sins, they are forgiven; if you do not forgive them, they are not forgiven."
Anointing the Sick (Extreme Unction)
-John 5:14:15 "Later Jesus found him at the temple and said to him, "See, you are well again. Stop sinning or something worse may happen to you." 15The man went away and told the Jews that it was Jesus who had made him well."
-James 5:14 "Is any one of you sick? He should call the elders of the church to pray over him and anoint him with oil in the name of the Lord."
Matrimony-Matt.19:10-11 The disciples said to him, "If this is the situation between a husband and wife, it is better not to marry." 11Jesus replied, "Not everyone can accept this word, but only those to whom it has been given."
-Eph. 5:31-32 "For this reason a man will leave his father and mother and be united to his wife, and the two will become one flesh." 32This is a profound mystery—but I am talking about Christ and the church."
-Acts 13:2-3 "While they were worshiping the Lord and fasting, the Holy Spirit said, "Set apart for me Barnabas and Saul for the work to which I have called them." 3So after they had fasted and prayed, they placed their hands on them and sent them off."
-1 Tim. 4:14 "Do not neglect your gift, which was given you through a prophetic message when the body of elders laid their hands on you."
-1 Tim. 4:16 "Watch your life and doctrine closely. Persevere in them, because if you do, you will save both yourself and your hearers."
There is my answer to the Baptist about the Seven Biblical Sacraments of the Catholic Church. All found in Holy Sacred Scripture, all instituted by Jesus Christ our Lord and Savior.