Da’wah is obligatory duty for Muslims. Allah speaks about Da’wah at various places in Quran: “We made you a middle nation to be witnesses over mankind.” (Surah al-Baqara, 143)
Islam is the perfect and complete religion for all mankind (Al-Maida:3).
Allah has guided the believers to the truth (Al-Baqara:213).
It is the only religion acceptable to Allah (Al-Imran:85).
“Let there be a community among you, who call to the good, enjoin the right and forbid the wrong. They are the ones who have success.” (Surah Al-’Imran, verse 104). “And warn your tribe and close ones.” (Surah al-Shura, verse 214). In these verses Allah commands to the muslims that Da’wah is an obligation on every Muslims.
In last sermon Prophet (PBUH) said; Convey what you have received from me, even it is a verse (Bukhari, Muslim Chapter on Hajj) This Hadith clearly indicates that you should not wait that one day you will become a scholar and then you will be able to do Da’wah. NO! But one should do Da’wah if he knows even a single verse of Quran or a single Hadith. You can give Da’wah at any time and any place, when one has an opportunity to do Da’wah at any place one should do it accordingly.