When Imaam Abu Dawood (rahimahullah) was asked as to why he had underwent the difficulty of leaving the ship and traveling to the shore to reply to the person who had sneezed, he replied, “It is possible that the person who sneezed is one whose du‘aas are readily accepted (and hence, if he replied, then this will be a means for me gaining hidaayat and forgiveness).”
That night, when the people aboard the ship went to sleep, they were told in a dream, “O people aboard the ship! Abu Dawood (rahimahullah) has purchased Jannah from Allah Ta‘ala in exchange of one dirham!” (Fat-hul Baari vol. 10, pg. 610)
Note:
The Sunnah practise is that when one hears someone sneeze and recite Alhamdulillah, then it is compulsory for one to reply to the sneeze by saying “Yarhamukallah”. Thereafter, it is also a sunnah for the person who sneezed to respond by saying “Yahdeekumullah” (may Allah Ta‘ala guide you) and “Yaghfirullahu lana walakum” (may Allah Ta‘ala forgive us and you).
Hence, Imaam Abu Dawood (rahimahullah) desired to practise upon the sunnah by replying to the person who sneezed, and he also desired to acquire the du‘aa of the one who sneezed. The reason is that it is possible that the one who had sneezed may be a pious person whose du‘aas are accepted, and through him replying and making du‘aa by saying “Yahdeekumullah” (may Allah Ta‘ala guide you) and “Yaghfirullahu lana walakum” (may Allah Ta‘ala forgive us and you), Imaam Abu Dawood (rahimahullah) would receive divine guidance in this life and forgiveness in the Hereafter.
Hence, Imaam Abu Dawood (rahimahullah) underwent the difficulty knowing the great reward that he would receive for practising upon the sunnah and becoming the means for the person who sneezed practising upon the sunnah. Similarly, he wished to receive the du‘aa which will assist him in this life by him receiving divine guidance, and assist him in the next life by him gaining forgiveness.
Hence, according to his expectation in the mercy of Allah Ta‘ala, Allah Ta‘ala accepted the du‘aa of the person and made it the means of Imaam Abu Dawood’s (rahimahullah) forgiveness.