The Best of the Nikmaat Ever Given to This Humanity is the Mercy of the Holy Prophet Muhammad SalaAllahu Alaihi Wasalam

 حدثنا ‏ ‏يحيى بن أيوب ‏ ‏وقتيبة ‏ ‏وابن حجر ‏ ‏قالوا حدثنا ‏ ‏إسمعيل وهو ابن جعفر ‏ ‏عن ‏ ‏العلاء ‏ ‏عن ‏ ‏أبيه ‏ ‏عن ‏ ‏أبي هريرة ‏أن رسول الله ‏ ‏صلى الله عليه وسلم ‏ ‏قال ‏ ‏من صلى علي واحدة صلى الله عليه عشرا ‏

Abu Hurayrah  reported Allāh's Messenger  as saying:

If anyone invokes a blessing on me once, Almighty  ALLAH  will grant him ten blessings.

[al-Bukharī and Muslim (from two narrators) narrated it from Abū Hurayrah . Also from Aħmad in his Musnad, Abu Dawūd in his Sunan, at-Tirmidhī and an-Nasā`i all from Abū Hurayrah. Another extended version to this narrated from Anas  from again al-Bukhārī in his Adab, Ahmad in his Musnad Nasa`i and al-Hākim in his Mustadrak, which added: "..and ten faults will fall from him and Allāh will raise him ten levels." Al-Hāfiz as-Suyūtī graded both hadīths authentic.]

من صلى علي من أمتي كتبت له عشر حسنات ومحيت عنه عشر سيئات

The Prophet  is reported to have said:

Whoever among my nation invokes blessings upon me, ten good deeds are written for him and ten sins are erased from him.

[Imām al-Ghazālī reported it in his Ihyā. Al-Haythamī reported it in his al-Zawā'id as did al-Bazzār and al-Hindī in his Kanz al-'Ummāl with a slightly different wording.]