Shabd is the Truth

Guru Nanak has described Shabd as Truth. This is because it never perishes. 

It is true from the beginning and has been true through the ages. It is True in the present and shall be True hereafter, oh Nanak.

Guru Nanak says:

He is One, and the Shabd is His insignia, He can be realised through a perfect Master.

 Basant M1, 1188-14

Both Guru Amar Das and Guru Arjan Dev support this:

He who loves the Truth, Loves the True Word too.

Sri Rag M2, 33-17

Listen to me, my friend and comrade; the Master has blest me with the Initiation of the True Shabd. 

Vadhans M5, 576—18