Genesis 4.8, the passage about the murder of Abel, never hints at what Cain used to kill him. Here are some of the translations:
New American Standard Bible (©1995)
Cain told Abel his brother. And it came about when they were in the field, that Cain rose up against Abel his brother and killed him.
GOD'S WORD® Translation (©1995)
Cain talked to his brother Abel. Later, when they were in the fields, Cain attacked his brother Abel and killed him.
King James Bible
And Cain talked with Abel his brother: and it came to pass, when they were in the field, that Cain rose up against Abel his brother, and slew him.
American King James Version
And Cain talked with Abel his brother: and it came to pass, when they were in the field, that Cain rose up against Abel his brother, and slew him.
American Standard Version
And Cain told Abel his brother. And it came to pass, when they were in the field, that Cain rose up against Abel his brother, and slew him.
Bible in Basic English
And Cain said to his brother, Let us go into the field: and when they were in the field, Cain made an attack on his brother Abel and put him to death.
Douay-Rheims Bible
And Cain said to Abel his brother: Let us go forth abroad. And when they were in the field, Cain rose up against his brother Abel, and slew him.
Darby Bible Translation
And Cain spoke to Abel his brother, and it came to pass when they were in the field, that Cain rose up against Abel his brother, and slew him.
English Revised Version
And Cain told Abel his brother. And it came to pass, when they were in the field, that Cain rose up against Abel his brother, and slew him.
Webster's Bible Translation
And Cain talked with Abel his brother: and it came to pass when they were in the field, that Cain rose up against Abel his brother, and slew him.
World English Bible
Cain said to Abel, his brother, "Let's go into the field." It happened when they were in the field, that Cain rose up against Abel, his brother, and killed him.
Young's Literal Translation
And Cain saith unto Abel his brother, 'Let us go into the field;' and it cometh to pass in their being in the field, that Cain riseth up against Abel his brother, and slayeth him.