It is narrated from Mujahid (may Allah have mercy on him): Do not say: "I made the crop grow," but say: "I sowed the seed; indeed it is Allah who makes it grow."
This is the saying of Mujahid; a marfu' hadith has also been narrated on this, but it is not strong.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب المزارعة / 11751