The Quraish notables came to Abu Talib and insisted that he put a stop to his nephew’s activities. Such activities if allowed unchecked, they said, would draw him into severe hostility. Abu Talib was deeply distressed at this open threat of his people and their enmity, but he could not afford to desert Mohammed (صلى الله عليه سلم) too. He sent for his nephew and told him what the people had said.
"Spare me and yourself and put not burden on me that I can’t bear."
Upon this the Prophet (صلى الله عليه سلم) thought that his uncle would let him down and would no longer support him, so he replied:
"O my uncle! by Allah if they put the sun in my right hand and the moon in my left on condition that I abandon this course, I would not abandon it until Allah has made me victorious or I perish therein."
The Prophet (صلى الله عليه سلم) got up, and as he turned away, his uncle called him and said, "Come back, my nephew," and when he came back, he said, "Go and preach what you please, for by Allah, I will never foresake you."
He then recited two lines of verse with significant meanings of full support to the Prophet (صلى الله عليه سلم) and absolute gratification by the course that his nephew had chalked out in Arabia.
Ibn Hisham 1/265,266 and Dala’il An-Nubuwwah by Al-Baihaqi 2/188. “The Sealed Nectar.”