(Aboo ‘Uthmaan said) “I found in the book of the Shaikh, the Imaam, my grandfather, aboo ‘Abdullaah Muhammad ibn ‘Adee Hamdawaih as-Saaboonee (rahimahullaah ta’aala), Abul-‘Abbaas, al-Hasan ibn Sufyaan an-Nasawee informed us that al-‘Abbaas ibn Sabeeh narrated to them (saying): ‘Abdul-Jabbaar ibn Taahir narrated to us (saying): Ma’mar ibn Raashid narrated to me (saying): I heard Ibn Shihaab az-Zuhree saying,”Teaching a sunnah is more superior than two hundred years of worship.”
Usool-u-Sunnah by Imam Ahmad ibn Hanbal (rahimahullaah), Chapter Six: The Distinguishing Signs of Ahlus-Sunnah
Meaning: 200 years of individual worship, like optional fasting and praying, since those deeds are for the one who performs them, and the reward for them would not increase over time, in contrast to someone who teaches a sunnah.
Teaching a sunnah is also a kind of worship, yet its reward is multiplied over time based on the number of people who practice what they learn, call to it, and teach it to others. So there is no specification of a reward of 200 here by Imaam az-Zuhree, rather he was giving an extreme example of the difference between two kinds of worship: one kind thats benefit is restricted to the one who performs it, and the other that has ongoing reward piling up based on the actions of the people who learned from the teacher, and those who learned from their students, and so on.
The Prophet (may Allaah raise his rank and grant him peace) said, what means, “Whoever invites to goodness will have a reward like all those who follow him in that, without their rewards decreasing in the least…” (Muslim)
Moosaa ibn John Richardson