Abu Wa'il said: This narration was related to me:
Sayyiduna Abu Bakr (may Allah be pleased with him) met Sayyiduna Talhah (may Allah be pleased with him), and Sayyiduna Abu Bakr (may Allah be pleased with him) asked: "Why is it that I see you troubled?" Sayyiduna Talhah (may Allah be pleased with him) replied: "It is about a word that I heard from the Prophet (peace and blessings be upon him). He (peace and blessings be upon him) said that this word makes (Paradise) obligatory, but I was not able to ask the Prophet (peace and blessings be upon him) about which word it was." Sayyiduna Abu Bakr (may Allah be pleased with him) said: "I know which word it is." Sayyiduna Talhah (may Allah be pleased with him) asked: "Which is it?" Sayyiduna Abu Bakr (may Allah be pleased with him) said: "It is La ilaha illallah (there is no god but Allah)."
Abu Ya'la recorded it, and its narrators are the narrators of the Sahih, except that Abu Wa'il did not hear it from Sayyiduna Abu Bakr (may Allah be pleased with him).
Hadith Referenceمجمع الزوائد ومنبع الفوائد / كتاب الإيمان / 3
Hadith Gradingمحدثین:إسناده ضعيف لانقطاعه
Hadith Takhrij«اخرجه الامام ابو يعلي فى مسنده 97 ، اورده المؤلف فى المقصد العلي 6 ، المطالب العاليه 48/3»