Does expiation or increasing the utterance of "Lā ilāha illā Allāh" (There is no god but Allah) become obligatory upon one who said "fertile land," believing that fertility is a cause and that Allah is the Bestower, and then regretted his saying?

You are not at fault, nor is expiation required, because of your correct belief that Allah Almighty is the true Bestower of blessings, and that the fertility of the land is a cause for abundant cultivation therein. In this situation, it is permissible for you to attribute a thing to its cause. Sheikh Ibn Uthaymeen mentioned that attributing a thing to its cause has three cases:

1. A hidden cause with absolutely no effect: Such as saying, "Were it not for such and such a saint, such and such would not have happened." This is major Shirk (polytheism).

2. A true cause proven by Islamic law or by sensory experience: This is permissible, provided that one does not believe the cause is effective in and of itself, and does not forget the Bestower of blessings.

3. An apparent cause not proven to be a cause by Islamic law or by sensory experience: This is a type of minor Shirk, such as amulets (Al-Tuwala) and necklaces that are said to prevent the evil eye, because it is establishing a cause that Allah has not made a cause.

This detailed explanation is supported by the Prophet's (peace be upon him) statement regarding his uncle Abu Talib: "Were it not for me, he would have been in the lowest depths of the Hellfire." We advise you to stay away from obsessive thoughts (waswas) in this matter and others, and to seek Allah's help in repelling the devil's cunning and whisperings, and not to surrender to them.