The fifth is the elongated hamzah, as in: “By Allah, I shall certainly do such-and-such.” The elongated hāʾ and hamzah may be used only with the Divine Name Allah.

As for the ruling on oaths: should a person swear an oath whenever he mentions something, or should he avoid swearing frequently?

We say: the basic principle is that one should not swear excessively, because Allah the Exalted says:

“Guard your oaths.” [5:89]

Some scholars explained this as meaning: Do not swear too often. Undoubtedly, this is preferable, safer for a person, and more conducive to freeing him from liability. Nevertheless, an oath may be prohibited, obligatory, recommended, or disliked.

It is obligatory when its purpose is to establish the truth. Thus, you must swear an oath when establishing the truth depends upon it. For this reason, Allah the Exalted commanded His Prophet to swear concerning three matters: that the Resurrection is true, that the Quran is true, and that the Hour will come.

Allah says:

“They ask you, ‘Is it true?’ Say, ‘Yes, by my Lord, it is indeed true.’” [10:53]

And He says:

“Those who disbelieve say, ‘The Hour will never come to us.’ Say, ‘Yes, by my Lord, it will certainly come to you.’” [34:3]

And He says:

“Those who disbelieve claim that they will never be resurrected. Say, ‘Yes, by my Lord, you will certainly be resurrected.’” [64:7]

Thus, when establishing the truth and reassuring the person being addressed depend upon an oath, the oath is obligatory.