Where in the Bible does it say?

It doesn't.

St. Matthew (13: 55) and St. Mark (6:3) do give the names of those it calls Jesus' "brothers," namely, James, Joses, Simon, and Jude. However, if you look at Matthew 27: 56 and Mark 15: 40 you will see both Evangelists tell us quite clearly that James and Joses were NOT sons of Mary or Joseph but children of a different "Mary" who is called both the Wife of Alphaeus/Cleopas AND the Virgin Mary's "sister." Now, it would have been highly unlikely in those days for two Jewish sisters to have the same first name, but obviously some close relationship is implied among all these people. It's really fairly easily solved: Alphaeus/Cleopas was the brother of St. Joseph, hence Alphaeus' wife, Mary, was the sister-in-law of the Virgin, making James, Joses, Simon, Jude, and the "sisters" to be Jesus' cousins. That the Evangelists call such cousins "brothers and sisters" isn't surprising but quite in line with Semitic thought where close kin were often called brothers/sisters.

Also, read John 19:25-27 (NJB): Seeing his mother and the disciple whom he loved standing near her, Jesus said to his mother, "woman this is your son." Then to the disciple he said, "This is your mother." Thus, Jesus gave away his mother to the care of St. John the apostle, which would be very strange and probably even illegal had Mary had children of her own who could have cared for her.

One must also take into account the almost universal belief of Christians throughout the ages that Mary, the Mother of Jesus, whom we call the God-bearer, was ever-virgin. The majority of the ancient Fathers of the Church believed Mary was ever-virgin, including Clement of Alexandria, Origen, and St. Jerome. Many Reformers did as well (surprisingly to most Protestants) including Luther, Calvin, Zwingli, and John Wesley.

OK... here is the scoop. Jesus was an only child and Mary remained a virgin her entire life. How do we know? Because first of all, a Jewish man of that era would never sleep with a woman that wasn't a virgin... that would be considered unclean. Second, we know that Mary even back then was referred to as the Ark of the New Covenant. The Jews would very well remember that nobody could touch the ark without penalty of death.

So why do so many Protestants get this wrong? Because there was no word specifically meaning brother or sister. The word used in the Bible means kinsperson and was interpreted as Brothers and sisters. It could very well have meant cousins.

Nowhere, of course. Mary had but one child in all her life an His Father was the Holy Spirit.

While many Protestants today seem to regard Mary’s perpetual virginity as a uniquely “Catholic belief,” it should be noted that the Protestant reformers Luther, Calvin, and Zwingli ALL professed this belief as well. The gospel writers’ used the Greek word “adelphos” (as a translation of the Hebrew “ah”), which could mean actual sibling brother (or sister in the feminine), but also means cousin, nephew, relative, etc. So the misconception (no pun intended) Mary had other children is easily avoided unless one is handicapped by the ignorant notion that the Gospel writer's actually wrote in King James' English 2000 years ago.

Mary had NO other children.

People fail to realize who is being spoken of in the verses below.

James and Joses are in Matthew, Mark, and John's Gospels referred to as the sons of Mary the wife of Clophas (Matthew 27:55, Mark 15:40, and John 19:25). Many early Church historians believe that Clophas and Joseph, Jesus' foster-father, were either brothers or cousins. Regardless, it does refer to Mary the wife of Clophas as the sister of Mary the mother of Jesus.

We can cross Simon off the list because Mark 3:18 tells us he is a Canaanite, "And Andrew, and Philip, and Bartholomew, and Matthew, and Thomas, and James the son of Alphaeus, and Thaddaeus, and Simon the Canaanite..."

Jude, we are told in Jude 1:1, is the "servant of Jesus Christ and the brother of James."

"Is not this the carpenter, the son of Mary and the brother of James and Joses and Judas and Simon, and are not his sisters here with us?" Mark 6:3-4

"Is not this the carpenter's son? Is not his mother called Mary? And are not his brethren James and Joseph and Simon and Judas? And are not all his sisters with us?" Matthew 13:55-56

Having been enlightened by an angel in a dream regarding her pregnancy, and perhaps further by Mary concerning the words of the archangel Gabriel to her at the Annunciation, Joseph knew that God had conducted himself as a husband in regard to Mary. She was now prohibited to him for all time, and for the sake of the Child and Mary he could only live with her in an absolutely chaste relationship.

Living a celibate life within marriage was not unknown in Jewish tradition. It was told that Moses, who was married, remained continent the rest of his life after the command to abstain from sexual intercourse (Ex 19:15) given in preparation the seventy elders abstained thereafter from their wives after their call, and so did Eldad and Medad when the spirit of prophecy came upon them; indeed it was said that the prophets became celibate after the Word of the Lord communicated with them (Midrash Exodus Rabbah 19; 46.3; Sifre to Numbers 99 sect. 11; Sifre Zutta 81-82, 203-204; Aboth Rabbi Nathan 9, 39; Tanchuman 111, 46; Tanchumah Zaw 13; 3 Petirot Moshe 72; Shabbath 87a; Pesachim 87b, Babylonian Talmud).

Joseph as celibate caretaker

As the recipient of the great revelation that what was conceived in the womb of Mary, his betrothed, was of the Holy Spirit and that the Child to be born was destined to save His people from their sins, surely Joseph knew that he was called to take care of Mary and her Child, the Messiah, for the rest of his life, which is why the angel told him to take Mary as his wife.

We may reasonable assume that Mary herself now shared with him all that the archangel Gabriel said to her. No less a Person than "the Son of God" (Lk 1:35) was to be entrusted to his care under the shelter of his humble home, now become the Holy of Holies.

Are these good enough for you?

Matthew 13:55 Is not this the carpenter's son? is not his mother called Mary? and his brethren, James, and Joses, and Simon, and Judas?

Mark 6:3 Is not this the carpenter, the son of Mary, the brother of James, and Joses, and of Juda, and Simon? and are not his sisters here with us?

Galatians 1:19 But other of the apostles saw I none, save James the Lord's brother.

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Funny............it never does.

Mary remained both sinless and a virgin her entire life

It doesn't. It only mentions Jesus' brothers and sisters.

Delusions: 4:24....