In Act IV Scene 1 Macbeth, having just heard that Macduff has escaped to England says, "The castle of Macduff I will surprise; seize upon Fife; give to the edge o' the sword his wife, his babes, and all unfortunate souls that trace him in his line." In the next scene we see this happening. Of course Macbeth himself is not there personally; it is his hired murderers who kill everyone in Macduff's family. Fife is the town where Macduff's castle is, since he is Thane of Fife.
Perhaps you are thinking of Lady Macbeth's line during her sleepwalking scene: "The thane of Fife had a wife--where is she now?"
Macbeth is first 'Thane of Glamis' then he is bestowed the title 'Thane of Cawdor' then king of Scotland
The first apparition warned Macbeth, 'Macbeth, Macbeth, Macbeth: beware Macduff, Beware the Thane of Fife. Dismiss me. Enough'
Duncan appoints him to that title, after it was stripped from the previous Thane. The former Thane of Cawdor was stripped of all titles and executed after joining a Norwegian invading force which was defeated at Fife. Macbeth at the time was at Forres, nowhere near Fife.
He must watch out for Macduff
Macduff, the Thane of Fife, kills Macbeth.
Fife
Lady Macbeth
The first apparition warned Macbeth, 'Macbeth, Macbeth, Macbeth: beware Macduff, Beware the Thane of Fife. Dismiss me. Enough'
dunsinane castle
When Macbeth refers to Macduff he is talking about a man who holds the title Thane of Fife.
Malcolm (Duncan's son) did not kill Macbeth, it was Macduff (Thane of Fife).
=Macduff The Thane of Fife=
There are a number of castles in the play: Forres, Inverness, Fife and Dunsinane. Inverness is actually Macbeth's castle.
Perhaps you are thinking of Lady Macbeth's line during her sleepwalking scene: "The thane of Fife had a wife--where is she now?"
Macbeth is first 'Thane of Glamis' then he is bestowed the title 'Thane of Cawdor' then king of Scotland
In Macbeth, important events that take place at Fife Castle include Macduff's discovery of Duncan's murder, Malcolm's testing of Macduff's loyalty, and the gathering of forces to overthrow Macbeth. It is also where Lady Macbeth's illness and eventual death occur.