His words, “at the time of slaughtering,” mean at the time of regular slaughter or nahr (piercing the lower neck). Thus, when performing regular slaughter upon an animal slaughtered in that manner, or nahr upon one for which nahr is prescribed, he must say, “In the name of Allah.” The grammatical analysis of this phrase has preceded: it is connected to an omitted verb, understood as coming after it and appropriate to the action. Thus, in regular slaughter one says, “In the name of Allah, I slaughter,” and in nahr, “In the name of Allah, I perform nahr.”
The evidence for this is the saying of Allah, exalted is He:
“Eat, then, of that over which the name of Allah has been mentioned, if you truly believe in His verses.” [al-An'am: 118]
And His saying:
“And why should you not eat of that over which the name of Allah has been mentioned, when He has explained to you what He has forbidden to you, except that to which you are compelled?” [al-An'am: 119]
And His saying, exalted is He:
“Do not eat of that over which the name of Allah has not been mentioned, for it is surely sinful disobedience.” [al-An'am: 121]
From the Sunnah is the Prophet’s statement, peace and blessings be upon him: “Eat whatever causes the blood to flow, provided that the name of Allah has been mentioned over it.” (1) He said, “Whatever causes the blood to flow...” Here, “whatever” is conditional.
One may also cite the hadith of Aishah, may Allah be pleased with her, narrated by al-Bukhari: Some people said, “O Messenger of Allah, people bring us meat, and we do not know whether they mentioned the name of Allah over it or not.” He replied, “Mention the name of Allah yourselves and eat.” (2) This indicates that it was already established among them that whatever had not had the name of Allah mentioned over it was not to be eaten. Hence they said, “We do not know whether they mentioned the name of Allah over it or not”—that is, should we eat it or not? So the Prophet, peace and blessings be upon him, said, “Mention the name of Allah yourselves and eat.”
His words, “In the name of Allah”: is what is intended this precise wording, or is what is intended the name of the One denoted by this name?