Hadith: There is no contagion, nor is there any evil omen in birds, nor is there any evil omen in the owl, nor is there any evil omen in Safar, and run away from the leper as you would run away from the lion

عَنْ أَبِي هُرَيْرَةَ رضي الله عنه قَالَ: قَالَ رَسُولُ اللَّهِ صَلَّى اللهُ عَلَيْهِ وَسَلَّمَ:
«لاَ عَدْوَى وَلاَ طِيَرَةَ، وَلاَ هَامَةَ وَلاَ صَفَرَ، وَفِرَّ مِنَ المَجْذُومِ كَمَا تَفِرُّ مِنَ الأَسَدِ».
[صحيح] - [متفق عليه] - [صحيح البخاري: 5707]

Abu Hurayrah (may Allah be pleased with him) reported: The Messenger of Allah (may Allah's peace and blessings be upon him) said:
"There is no contagion, nor is there any evil omen in birds, nor is there any evil omen in the owl, nor is there any evil omen in Safar, and run away from the leper as you would run away from the lion."
[Authentic hadith] - [Narrated by Bukhari & Muslim] - [Sahih Bukhari - 5707]

Explanation

The Prophet (may Allah's peace and blessings be upon him) clarified some of the practices of Jāhliyyah (the pre-Islamic era of ignorance) by way of warning and stressing the fact that all matters are in the Hand of Allah and nothing occurs except with His command and decree. These practices are:
First: The people of Jāhliyyah used to think that a disease was contagious by itself. However, the Prophet (may Allah's peace and blessings be upon him) forbade such a belief that a disease could be naturally transmitted from one sick person to another, as Allah is the Disposer of the universe and the One Who sends down the disease and lifts it, and this only occurs according to His will and decree.
Second: The people of Jāhliyyah used to make a bird fly when setting out on a journey or for trade. If the bird flew towards the right, they would take that as a good omen, but if it flew towards the left, they would consider this an evil omen and would return. The Prophet (may Allah's peace and blessings be upon him) forbade such an act of taking birds as a bad omen and made it clear that it is a false belief.
Third: The people of Jāhiliyyah used to say that if an owl fell on a house, its dwellers would be stricken by a disaster, but again the Prophet (may Allah's peace and blessings be upon him) forbade taking this as an evil omen.
Fourth: He forbade taking the month of Safar, which is the second month in the lunar calendar, as a bad omen. It is said that "Safar" is: a snake in the stomach that affects cattle and people, claiming that it is more contagious than scabies; however, he negated such a belief.
Fifth: He commanded that one should move far from the leper as he would move far from the lion as a precaution and to seek one's safety and utilize the available means as commanded by Allah. Leprosy: a disease that eats away a man's organs.