Iyas bin Salama bin al-Akwa reported that his father reported to him that he heard Allah's Apostle (ﷺ) as saying: A person sneezed in his presence and he said to him: May Allah have mercy upon you. And he then sneezed for the second time and Allah's Messenger (ﷺ) said to him: He is suffering from cold (and no response is necessary).
Hadith Referenceصحيح مسلم / كتاب الزهد والرقائق / 2993
Hadith Commentary:Benefits and Issues: If sneezing occurs due to a cold, then one supplication is sufficient; in normal circumstances, the Prophet (sallallahu alayhi wa sallam) has supplicated three times.
Source: Tuhfat al-Muslim: Commentary on Sahih Muslim, Page: 7489
´Narrated Iyas bin Salamah:` from his father: "A man sneezed in the presence of the Messenger of Allah (ﷺ) while I was present, so the Messenger of Allah (ﷺ) said: 'Yarhamukallah (May Allah have mercy upon you).' Then he sneezed a second and third time. So the Messenger of Allah (ﷺ) said: "This man is suffering from a cold.'"
Shaykh Dr. Abdur Rahman Freywai
Explanation: 1: From this it is understood that there is no need to respond after someone sneezes once or twice or more times.
Source: Sunan al-Tirmidhi – Majlis ‘Ilmi Dar al-Da‘wah, New Delhi Edition, Page: 2743
Salamah bin al-Akwa said: when a man sneezed beside the prophet ﷺ, he said to him: Allah have mercy on you, but when he sneezed again, he said: The man has a cold in the head.
Shaykh Umar Farooq Saeedi
Benefits and Issues: ➊ It is obligatory to respond to the first sneeze. ➋ After that, it is not obligatory, as is also indicated by Sahih Muslim. See: (Sahih Muslim, Kitab al-Zuhd, Hadith: 2993)
Source: Sunan Abu Dawood – Commentary by Shaykh Umar Farooq Saeedi, Page: 5037