Ibn 'Abbas reported: Allah has prescribed the prayer by the tongue of your Apostle (صَلَّی اللَّهُ عَلَيْهِ وَسَلَّمَ) as two rak'ahs for the traveller, four for the resident, and one in danger.

Abu Burda reported: I visited Abu Musa, as he was in the house of the daughter of Fadl bin 'Abbas. I sneezed but he did not respond to it (by saying): Allah may have mercy upon you. Then she sneezed and he (Fadl bin 'Abbas) said: May Allah have mercy upon you. I came back to my mother and informed her about it, and when he came to her she said: My son sneezed in your presence and you did not say: "Allah may have mercy upon you, and she sneezed and you said for her: "May Allah have mercy upon you." Thereupon he said: Your son sneezed but he did not praise Allah and I did not beg mercy of Allah for him and she sneezed and she praised Allah and so I said: May Allah have mercy upon you, as I heard Allah's Messenger (ﷺ) as saying: When any one of you sneezes he should praise Allah and the other should say: May Allah have mercy upon you, and if he does not praise Allah, no mercy should be begged for him.