as Salam alaykum.

Did prophet forget anything? As a Ahlesunnah, we do believe he didn’t forget anything from revelation, or any shariah related issues.

As for shias?

مختصر البصائر – الحسن بن سليمان الحلى – ص 284 – 285
 وعنه ومحمد بن الحسين بن أبي الخطاب وغيرهما عن أحمد بن محمد بن أبي نصر ، عن هشام بن سالم ، عن سعد بن طريف الخفاف ، قال : قلت لأبي جعفر ( عليه السلام ) : ما تقول فيمن أخذ عنكم علما فنسيه ؟ قال : ” لا حجة عليه ، إنما الحجة على من سمع منا حديثا فأنكره ، أو بلغه فلم يؤمن به وكفر ، فأما النسيان فهو موضوع عنكم . إن أول سورة نزلت على رسول الله ( صلى الله عليه وآله وسلم ) * ( سبح اسم ربك الأعلى ) * فنسيها ، فلم يلزمه حجة في نسيانه ، ولكن الله تبارك وتعالى أمضى له ذلك ، ثم قال  سنقرئك فلا تنسى “.

Translation:

“Mukhtasar al-Basair” by al-Hasan ibn Sulayman al-Hilli, pages 284-285.

“And from him, and from Muhammad ibn al-Husayn ibn Abul Khattab and others, from Ahmad ibn Muhammad ibn Abu Nasr, from Hisham ibn Salim, from Sayyed ibn Tareef al-Khaffaf, which said: I asked from Abu Jafar (alaihi salam): “What do you say about person who took knowledge from you and forgot?” He said: “No argument against him for this, argument against man who heard hadith from us, and rejected it. Or it (hadith) was narrated to him and he didn’t believe it, and disbelieved (by this). As for forgetfulness, it is (known) thing from them. First chapter (surah) revealed upon prophet (sallalahu alayhi wa alihi) was – “Glorify the name of thy Guardian-Lord Most High” (87/1), and HE FORGOT IT, (but) there was no need for him an argument in forgetting it, but Allah blessed and exalted arrange this for him, then said (by saying?): “We will make you recite so you shall not forget” (87/6).