Shaikh Ibn ul-‘Uthaymeen (may Allah have mercy upon him) wrote:

“(I bear witness): I affirm in my heart and profess on my tongue

(That there is no Deity worthy of worship): Deity means (مألوه), which is that which is worshiped with love and veneration.

So La ilaha illallah means: “There is no Deity worthy of worship in truth except Allah, the Exalted (لا معبود حق إلا الله)”. So the testimony here is a testimony on the tongue and a testimony in the heart. So the testimony does not suffice on the tongue except if done apparently in the worldly life. And the testimony in the heart [alone] does not suffice. Rather it is necessary to articulate it. Otherwise a person will not make sacred his blood and wealth because no one knows what is in the heart except Allah. The khabr (لا) [in this statement] is used for denial along with an attached implicit word. The attached implicit word is: “in truth” and this is the correct Taqdeer. This is because this attached implicit word is indicated in the Noble Quran. Allah, the Exalted said:

ذَلِكَ بِأَنَّ اللَّهَ هُوَ الْحَقُّ

That is because Allah, He is the Truth

[22:6]

As for the attached implicit word being (بحق), then this is in order to bring [the meaning of this statement] closer to the public. However, if we make the attached implicit word be the word (حق), then that is clearer and more explanatory. If we are made the attached implicit word be the word (بحق), then we would need to make a second attached implicit word which is attached to a preposition phrase
(جار ومجرور). So the meaning then would be: “there is no deity that exits and deserves worship in truth [except Allah]”. It is well-known that any time an attached implicit word in a sentence is smaller in number, then it is more deserving [to be used]”

[Ta’leeq ‘ala al-Qawaaid wa Usool al-Jaami’ah (pg. 12-13)]

The Shaikh (May Allah have mercy upon him) mention the same opinion in Explanation of his Book Aqeedah Ahlus-Sunnah wal-Jam’aah (Tape no. 1 Side B) and also in his Tafsir of Surah as-Saffat (Tape no. 4 side B)

And Allah Knows Best

Faisal bin Abdul Qaadir bin Hassan
Abu Sulaymaan