This takes place in act 2, scene 3 of William Shakespeare's Macbeth.
Macduff arrives at Macbeth's castle early in the morning to meet with King Duncan but instead discovers that Duncan has been murdered. Macduff raises the alarm, and within minutes, the castle's courtyard is full of shocked and dismayed people, including Macbeth, Lady Macbeth, Macduff, Lennox, Ross, and Banquo. The last to arrive in the courtyard are Duncan's sons, Malcolm and Donalbain.
Malcolm and Donalbain are quickly told about their father's murder, and Malcolm and Donalbain just as quickly decide that standing around in the courtyard is not where they want to be. They're getting suspicious looks from the others, and they're also thinking that, as Duncan's sons, they might be next in line to be murdered...
DONALBAIN: What should be spoken here,
where our fate,
Hid in an auger-hole, may rush and seize us? [2.3.136–138]
Malcolm and Donalbain decide that it's not safe to stay in Scotland:
DONALBAIN: Where we are
There's daggers in men's smiles . . . [2.3.160–161]
They decide to split up and leave the country—Malcolm to England, and Donalbain to Ireland.
Donalbain's next lines express his suspicions about who he thinks murdered his father . . .
DONALBAIN: . . . the near in blood,
The nearer bloody [3.2.161–162].
The nearest in blood to Malcolm and Donalbain is their cousin, Macbeth, whom they suspect murdered Duncan.
A verse in the Bible that would have been familiar to Shakespeare's audience comes very close to the meaning of Donalbain's lines:
And a man's foes shall be they of his own household. [Matthew 10.36, Bishop's Bible*]
Malcolm and Donalbain reasoned that if Macbeth murdered Duncan, he wouldn't hesitate to kill Duncan's sons in order to secure his throne.
* The Bishop's Bible was the Bible in general use in England prior to the King James Version, which was published in 1611, about eight years after Macbeth was first performed. A revised edition of the Bishop's Bible was published in 1602, a year before Macbeth was performed, and would have been very familiar to Shakespeare's audience.