Muhajir bin Qunfud reported,
He came to the Prophet ﷺ while he was relieving himself and greeted him, but the Prophet did not return the greeting until he had performed ablution. Then he apologized to him, saying, "I disliked mentioning the name of Allah 
except in a state of purity," or he said, "in a state of purification."
Abu Dawud 17
Daifحدثنا محمد بن المثنى حدثنا عبد الأعلى حدثنا سعيد عن قتادة عن الحسن عن حضين بن المنذر أبي ساسان
عن المهاجر بن قنفذ
أنه أتى النبي ﷺ وهو يبول فسلم عليه فلم يرد عليه حتى توضأ ثم اعتذر إليه فقال إني كرهت أن أذكر الله عز وجل إلا على طهر أو قال على طهارة
[Its chain of transmission is daif] Nasai narrated it in the Book of Purification, chapter on returning the greeting after wudu, hadith no. 38, and Ibn Majah narrated it, no. 350, from the hadith of Saeed bin Abu Aruba with the same wording. Ibn Khuzayma graded it sahih, hadith no. 206, as did Ibn Hibban (Mawarid, no. 189), and Hakim, 12/167 and 3/479, saying it meets the criterion of the two Shaykhs, and Dhahabi agreed with him.Hasan Basri conceals gaps in his chains of transmission, and he narrated this using the ambiguous formula "an". However, the basic hadith has supporting witnesses, apart from the phrase "until he performs wudu."