Is saying, “Proclaim His Oneness,” or “Proclaim the Oneness of Allah,” and responding with “There is no god but Allah,” part of the guidance of the Righteous Predecessors?

There is no objection to this matter, as it falls under the general evidence commanding the remembrance of Allah Almighty and assisting in it, such as His saying, "O you who have believed, remember Allah with much remembrance" (Quran 33:41), and the saying of the Prophet (peace be upon him), "The example of one who remembers his Lord and one who does not remember his Lord is like that of the living and the dead." However, one must not adopt this as a habit believed to be a fixed Sunnah in its description and timing, for that would be considered an innovation (bid'ah).