On the Night of Isrā', two cups were brought to the Prophet, (may Allah’s peace and blessings be upon him)
Authentic hadithعن أبي هريرة رضي الله عنه : أنّ النبيَّ صلى الله عليه وسلم أُتِيَ لَيْلَةَ أُسْرِيَ بِهِ بِقَدَحَيْنِ مِنْ خَمْرٍ وَلَبَنٍ، فَنَظَرَ إِلَيْهمَا فَأَخَذَ اللَّبَنَ. فَقَالَ جِبريل: الحَمْدُ للهِ الَّذِي هَدَاكَ لِلفِطْرَةِ لَوْ أخَذْتَ الخَمْرَ غَوَتْ أُمَّتُكَ.
Abu Hurayrah (may Allah be pleased with him) reported: Two cups of wine and milk were presented to the Prophet (may Allah's peace and blessings be upon him) on the Night of Isrā' (the night journey to the Aqsa Mosque). He looked at them and took the milk. Jibrīl said: "Praise be to Allah, Who guided you to the Fitrah. Had you taken the wine, your Ummah would have gone astray.”
Explanation
Jibrīl presented two cups to the Prophet (may Allah's peace and blessings be upon him) on the Night of Isrā' and Mi’rāj refers to his night journey to the Aqsa Mosque in Jerusalem and his ascent to heaven, one filled with wine and the other with milk. “He looked at them,” meaning: as if he was asked to choose between them. “He took the milk,” meaning: he received inspiration to choose the milk. Jibrīl said: “Praise be to Allah, Who guided you to the Fitrah,” meaning: you chose the sign of Islam and uprightness. Milk was made a sign of that because it is pleasant, pure, palatable, and of no evil consequences. (And then he said:) “Had you taken the wine, your nation would have gone astray."
Source · Narrated by Bukhari & Muslim
From the Hadith Encyclopedia (hadeethenc.com).