It is narrated from Sayyiduna Jabir (may Allah be pleased with him) that the Prophet (peace and blessings be upon him) came and said: When any one of you is praying, he should not spit to his right side, but rather to his left side or under his foot.
Hadith Referenceمسند احمد / مسند المكثرين من الصحابة / 14625
Hadith Gradingحکم دارالسلام:صحيح لغيره، وهذا إسناد ضعيف من أجل ابن لهيعة، لكنه متابع، وأبو الزبير لم يصرح بسماعه من جابر، وانظر: 14470 و 15260