On the authority of Ḥudhayfah (may Allah be pleased with him), from the Prophet ﷺ who said: “Do not say, ‘Whatever Allah wills and whatever so-and-so wills,’ but rather say, ‘Whatever Allah wills, then whatever so-and-so wills.’” ⦗1⦘ It was transmitted by Abū Dāwūd with a sound chain of narrators.

It was also reported from Ibrāhīm al-Nakhaʿī that he disliked a person to say, “I seek refuge with Allah and with you,” but allowed him to say, “With Allah, then with you.” He further said, “Say: ‘Had it not been for Allah, then for so-and-so,’ but do not say: ‘Had it not been for Allah and so-and-so.’”

— Grammatical notes —
• lā taqūlū: lā is a prohibitive particle; the verb following it is in the jussive mood, marked by the omission of the final nūn.
• mā shāʾa-Allāh wa shāʾa fulān: the conjunction with the letter wāw implies coupling and equivalence.
• mā shāʾa-Allāh thumma shāʾa fulān: the conjunction with thumma implies sequence and delay.
• yukrahu: in the usage of the early Muslims, karāha (“dislike”) denotes prohibition.
• aʿūdhu: al-ʿawdh means to seek shelter with and rely upon another.
• lawlā: a particle indicating the non-occurrence of something because of the existence of something else.

Overall meaning of the report:
The Prophet ﷺ forbids attaching the name of a created being to the name of the Creator with the particle wāw after mentioning will and similar concepts, because the item joined by wāw is treated as equal to what precedes it; the particle was coined for simple juxtaposition, so—