"She put her hand to the tent peg" (Judges 5:26). The word "hand" [used by itself] means none other than the left hand, as it is said, "My hand also has laid the foundation of the earth, and My right hand has spanned the heavens" (Isaiah 48:13). And it says, "Why do You withdraw Your hand, even Your right hand?" (Psalms 74:11). And it says, "And it shall be for a sign upon your hand" (Exodus 13:16) [where the tefillin are bound upon the left arm].
Her Hand to the Tent Peg and the Meaning of the Left Hand
Yalkut Shimoni on Nach 56:1
ידה ליתד תשלחנה. אין יד אלא שמאל שנאמר אף ידי יסדה ארץ וימיני טפחה שמים, ואומר למה תשיב ידך וימינך, ואומר והיה לאות על ידכה: